SirPoonga, which stage did you start with on your Gentoo install?  starting from stage one took me like a week to get through it (on a P120).  next time I'll start from either stage3 or the GRP.
If you are ever looking to pick up a cheap used computer (and you have to actually pay for it), knoppix (or knoppix-mame or AdvanceCD) is good to have with to see if the machine will handle mame.  I imagine without too much work, a bootable FreeDOS running Vantage and ArcadeOS would be nice as well.
Personally, my favorite is AdvanceCD for this purpose.  That CD and a portable CP and you can have an instant Mame party (especially if you are going to be trapped at the in-laws for a few days.