you have to start that young?! crap!!!

but yeah, there are some fixed gear bikes at the bike polo games here with a ratio of maybe 1.5:1, and you can get some mad skids with those.

as far as bmx cranks...i know most chainwheels are pretty small, but i know i can get them up to 44t, which is about what i like...i have 43x17 now and love it. i just have to figure out bb compatibility, chainline, etc.