Exploder mentioned AntiX a while back in a thread. It is based on Mepis, and might work just fine on the hardware you have. If you check http://antix.mepis.org/index.php/Main_Page
, you can see if AntiX might be what you need. In my testing of AntiX, everything with which I fiddled on the Live CD worked great. Their forum is similar to this one with a small and helpful community. AntiX is worth your time to look into.
I agree that 128 MB of RAM is going to be the problem with running Mint. I know Mint Xcfe will run great on a machine with 256 MB of RAM, but I have not tried it on a machine with 128 MB. You might have a go at it just for verification purposes. If you could run across another 128 MB stick of RAM someplace, the whole experience would be better.
The Mint Fluxbox version looks interesting, but I have not tried it yet. That is also an avenue to explore.
Good luck, and please post back with your results. Have fun!