It seems a developer (Codemonkey) of both game is reworking them to work better on modern systems, go see here and download them!:

Rollcage -> Rollcage Redux: http://www.codemonkey.me.uk/view_blog_entry.p … og_entry_id=131
Rollcage Stage II -> Rollcage Extreme: http://www.codemonkey.me.uk/view_blog_entry.p … og_entry_id=132

He plans to re-work Stage II to use physics of the original, which would be interesting.

Redux discussion: http://steamcommunity.com/groups/rollcage/discussions/3/
Redux builds: http://steamcommunity.com/groups/rollcage/discussions/2/

Extreme discussion: http://steamcommunity.com/groups/rollcage/discussions/7/
Extreme builds: http://steamcommunity.com/groups/rollcage/discussions/6/