What bottom bracket to buy?
 

Hey, I'm looking to build up a nice fixed gear conversion. I've got a frame and its a Pinarello road frame - 1990s vintage.

I need to buy a bottom bracket. Any recommendations?

what crank?

good question, but i haven't decided.

should i buy the BB and cranks at the same time? i need to figure out the gearing i want, and was going to spend some time finding some cool looking cranks. i was thinking I could just buy a dura ace or record BB and plug it in. But i'm not sure of the exact size BB i need, and i'm only assuming it's italian thread.

choose bb/cranks/rear hub at the same time and match the chainline up for each. for a rear hub chainline of 42, campy cranks and some other italian cranks (gipiemme i know for sure, maybe others) usually need 111 symmetrical bb. japanese usually go 109. someone correct me if i am wrong ont his.

do i need to worry about hte chainring or cog at the beginning or can i wait? obvoiusly lots of cranks come with rings, so that would be cool. . but what i assume is that there must be a special spindle which need to mate the crank with the BB, and thus those two pieces need to be purchased up front.

Whatever your crank is, there is a BB that it will work with. However, knowing what kind of threading your frame has in the BB shell will make your choosing easier too.

Chainring and cog: You'll want to get your chainring after your crank, and your cog after your hubs. Chain after both.

The spindle issue:

Square tapers are the most common, and something like 99% of the tapers for any square taper set will match. There are Octalink and ISIS BBs that interface only with the respective cranks, and these are stiffer for more power transfer, but everything is more expensive.

...but there's ISO and JIS tapers in the square taper world. Watch out for that.

Like el twe says, more like a 60-40 shot instead of 99%. ISO is on Campy, Miche, Paul, and some others. JIS is most of your Japanese brands (Shimano, Sugino, Hatta, etc.).
Actually it's about the same price, but unless you get track specific parts, there is a lot less variation in spindle length (usually just one or two) for each BB, so getting your chainline right is a lot harder.