If you tell us what you already have (frame, crank, rear hub,...) that would help.
Theres alot of nice cranks you could get, i like Sugino personaly.
Spoke lenght varies for different setups, you problably need shorter spokes, take you rims and hubs to your lbs, they will tell you what spoke lenght you need.
Your cog is problably 1/8", you need a new chain.
Read this:
http://sheldonbrown.com/fixed.html
and this:
http://sheldonbrown.com/wheelbuild.html
and then this:
http://www.sheldonbrown.com/gloss_bo-z.html#bottom