I hope that's meant to be 0.5GB, right? :)
With that layout I wouldn't bother too
much about sub-dividing, really. Try
/dev/hda1 ext2 /boot 32MB
/dev/hda2 swap (??? MB)
/dev/hda3 reiserfs /var (REST)
/dev/hdb1 reiserfs / (ALL)
If you find you're running out of space
on root you can still for example
have tmp in /var, and make it a
symlink in /
Cheers,
Tink