with the outboard bearings, you can't just grab a different bottom bracket. however, if you are doing a conversion (or anything with a 126 or 130 mm rear spacing, you have the ability to move the chainline between 6 an 10 mm, respectivly, in order to get it straight. normally, within 2 or 3 mm is acceptable. you will probably have to fiddle with the rings on the inside or the outside of the crank, and use a few different washers. i have not used one on a fixed gear, but don't see any major issues as long as you aren't chainline anal.

that 105 crank you linked does not include a bottom bracket, so be ready to factor in another $40, and at that price you are back into seguino 75 territory, hardly worth it in my opinion. check out the for sale forums of this board and craigslist in your local area for real deals, or if you can a bike co-op. we sold a set of ultegra cranks (used, but decent shape- octalink bb) for $35. i picked up my square taper 105's for $20, but they aren't shiny at all.

I am running an 80's 105 road double (square taper), with a zen messenger ring on the inside crankarm. have no idea what spacing bb came on the bike, but it lines up damn near perfect with my surly cog on a formula hub. now, i have had friends who have tried all sorts of crap trying to get theirs reasonably straight, but mine just worked fine.