First of all, let's consider Riley as the Spurs coach.
Riley takes over in 2000, and sees that he has Duncan and Robinson - two players which fit in to what Pat Riley wants to do with a team - establish a top level threat in the post, and a top-level threat on the perimeter. Beyond that, it's defense, defense, defense. And the 2000 Spurs have the defense. Avery Johnson is ousted as the starting point guard, favoring Antonio Daniels first, and then, toward the end of the year, Terry Porter. Unfortunately, due to Duncan's injury, and the wear-and-tear on Robinson and Elie from Riley's practices, the Spurs are ousted in the playoffs.
In 2001, acquisition of Derek Anderson makes him Riley's pet project. Derek Anderson ends up with a career year, and Duncan returns healthy. Unfortunatley, Robinson is done. He misses 15-to-20 games. Riley's point guard crew is in terrible shape - Daniels has taken over as the starter again, but Riley's not really happy with him. Porter is on his las legs, as is Avery Johnson. Perhaps San An is good for a finals appearance, but, in the end, the Sixers run them out of the building.
In 2002, the Spurs are hurting. David Robinson and Terry Porter retired after last season. The team didn't trade Derek Anderson for Steve Smith. Malik Rose takes over as the starting power forward, Duncan moves to center. Rookie point guard Tony Parker infuriates Riley, who is still playing Antonio Daniels as the starter at point. Newcomers Steven Jackson and Bruce Bowen battle for the small forward spot, with Bowen winning the battle. As the season goes on, Anderson falls further and futher out of favor, eventually being replaced by Stephen Jackson. The Spurs become very reminiscent of Riley's Knicks - brutal and bruising. Unfortunately, their talent is depleting. By post-season, Duncan has been absolutely brutalized.
In 2003, Riley is interested in rookie guards Manu Ginobilli and Devin Brown, but is still starting the Jackson/Bowen combo. In an experiment, Riley plays Anderson at the point. It fails. He plays Parker at the point. He's not happy. Speedy Claxton finally settles into the point guard role. However, a lack of depth up front prevents the Spurs from making significant noise in the playoffs.
In the 2003 off-season, after seeing the team fall short time and time again, with a lack of development of any young players, Anderson rotting away on the bench, and with Duncan being exhausted, Pat Riley is fired.
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Popovich with the Lakers.
2000 - Shaquille O'Neal comes up with the MVP year that everyone has expected him to have for eons. O'Neal responds extremely well to Popovich's military-style. Kobe Bryant, however, doesn't. With a line-up of Derek (not Ron) Harper at the point, Kobe at the 2, Rick Fox at the 3, A.C. Green at the 4, and O'neal, the Lakers power through the playoffs and defeat the Pacers soundly.
2001 - Shaquille O'Neal continues to terrorize the league, as the one and only captain of the team. Kobe Bryant is rebelling openly against Popovich, who is pressuring Laker management to trade him. The off-season swap for Horace Grant didn't happen, and the new line-up of O'Neal, Travis Knight, Fox, Bryant, and Derek Harper/Derek Fisher again powers through the league. Of big interest to Popovich is Tyronn Lue, who figures to play a more prominent role next season.
2002 - The Shaquille O'Neal/Kobe Bryant feud, which we've seen coming for years, erupts - and like NOTHING we've seen in real life. Popovich responds strongly against Bryant, resulting in a motivated O'Neal, and disgruntled Bryant, and a Laker failure in the playoffs. In the off-season, Jerry West - who has been with the team the entire time - works diligently to trade Bryant, believing that he's got something special coming up in Devean George. West's hope is to get a power forward/2-guard combo in exchange for Bryant. However, West strikes the gold mine - he acquires Kevin Garnett for Kobe Bryant, Travis Knight, Tyronn Lue, and a draft pick.
2003 - Despite having a great deal of talent, the Lakers struggle because of Garnett's failure to respond to Popvich, and the team's aged back-court, which now starts Glen Rice at the 2-guard. Devean George looks good, though.
2004 - After acquiring Gary Payton as a free agent, the Lakers return to dominance, and win the championship, with a line-up of O'Neal, Garnett, George, Rice, and Payton. Garnett still isn't happy about Popovich. And Shaq is showing signs of age.
That's about as far as I can realistically go. I'm having trouble figuring out who Jerry West is going to acquire for the backcourt.
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Phil and the Spurs:
2000 - Phil finds a team he can use - mostly. Avery Johnson must go. Terry Porter emerges as the starter, with Steve Kerr and Antonio Daniels seeing minutes. Jaren Jackson continues his torrid streak from the previous playoffs, and replaces Shawn Elliott in the starting line-up. The athletic system Phil puts in place, however, means that Robinson is coming back from injury right as Duncan goes down in the playoffs. A first-round casualty.
2001 - New acquisitions Derek Anderson and Danny Ferry fit the triangle perfectly. Terry Porter is still starting at point. Avery Johnson is gone. The starting line-up is Porter, Anderson, Jaren Jackson, Ferry, and Duncan, with Robinson coming off the bench. The Spurs lose in a close series to the Lakers in the Western Conference Finals. Duncan terrorizes the league, and narrowly loses to Shaquille O'Neal in the MVP voting.
2002 - The Derek Anderson/Steve Smith trade doesn't happen. Injury problems continue to plague Robinson. Ferry is breaking down. New acquisition Stephen Jackson looks like a fit to the triangle, but takes to it very slowly. Bruce Bowen swipes the small forward job, with Anderson now playing point, and Jaren Jackson at the 2. Tony Parker wasn't drafted. Due to the weakness at the power forward spot - Malik Rose isn't cutting it for Jackson and Ferry is breaking down, the Spurs are eliminated in the playoffs by the eventual champs - the Sacramento Kings. Duncan has another great year, but O'Neal wins his third straight MVP.
2003 - Robinson retired in the off-season. Jaren Jackson goes down with injury. Interesting rookie Manu Ginobili gets a few looks, but Phil decides he won't work out at the point. Devin Brown sees significant minutes in place of Jackson. Anderson and Bowen have good years, as does Duncan, but the power forward spot is now a gaping hole. San An is eliminated by Dallas - the eventual champs - in the playoffs.
That's about as far as I can go. I don't know what the power forward solution is, and I'm stretching how far I'm willing to go with Derek Anderson.