Not quite, in WinME you've got two things happening, an update (of sorts) and the removal of real mode DOS. The removal of DOS, I guess is to prepare the public for XP, a real non-DOS OS (XP probaly has some kind of DOS support just the OS use it to run). Most newer games should be ok, some older DOS games (that relied on customized config and autoexec files) may not be. The update did change several things; one being it came with DX8, another the names of some of the registry keys. The versions of DirectX are supposed to be backwards compatible, the registry keys, (well if the game needed one of the old key names there may be a patch or update for it) seem to mostly be related to drivers (at least the differences I've seen). The few games I've tried in both OSs worked about the same, and the installs went off without a hitch. Unless your looking at some really old DOS based games, then you should be ok, but be on the look out for strangeness. You can also check each game's website and see if there are any patches for ME or maybe anything that needs to be specially configured.
Links list:Computer Links
Do Vulcans even have to debug?