Which codec?

I’ve got the following system :
Pentium 3 450Mhz , 256MB RAM etc.

Which codec should i use to have good results in less time ?
DivX 5.1 , DivX 3.11 , Xvid or something else ?

Where will i have faster encoding , on Windows XP or 98 ?

DivX 5.1 will give you better results but will take more time. This is over 3.11. Sorry I have no info on Xvid.

I tend to use Windows XP over 98. It seems to work better for me but I have no evidence for that theory. Just one of those feelings.