WMNicEnc
For correct VC-1 encoding, you need to have WMP11 or the WMF11 SDK installed - which means you more or less need at least XP SP2 or Vista; it's possible to deconstruct the archive and register the .dll files manually, but you'd need to know which are which and there's still no guarantee the right ones would work. For any of the other WMV formats, though, you can get by with WMP10.
ffdshow also has WMV encoding options in its VFW, but I wouldn't use them myself.