I think that Speeddog is pretty much on the money.
As far as frame/chassis components go, there are 4 main eras for the monster.
The 1993-1999 Monsters are relatively similar. Same frames, tanks, seats, etc. There are minor changes between years, but even a well trained eye will have trouble telling the difference without serious investigation.
2000-2001 were transitional years for Monsters
In 2000, the M900 got fuel injection. All the Monster's tanks and seats changed a bit, and the front brake and fender mounts and front axle size changed, and the 'suicide stand' was replaced with the sidestand ignition interlock. The frames and swingarms on these bikes were still as derived from the 851/888 series.
In 2001, the M600 arrived in the US, the M750 got an extra front brake and a tach, and the 4-valve watercooled Monster S4 arrived with it's ST4 derived frame, swingarm, and suspension.
For 2002, the smaller displacement Monsters got fuel injection, The M600 became the M620 i.e., and the 2-valve monsters got the ST-type frames, swingarms, suspension components and chassis electronics similar to the 4-valve Monster S4.
2003 brings the last of the major changes in frame/chassis with the introduction of the S4R and it's single sided swingarm and other chassis/suspension changes that go with it. A similar set-up would follow to the 2-valve, air-cooled Monsters with the S2R. The M750 and M900 were bumped to 800s and 1000s respectively.