Steam Help

Not getting much help at UPN, so I'll ask here since Sean and Matt seem to be popping in every once in a while.

I installed Steam last night for the first time ever, but did so to my C:\ partition (60 GB) by mistake instead of my D:\ partition (500 GB). Obviously this became an apparent problem when The Orange Box asked to occupy 15 GB of space. I'd happily let it keep 15 GB permanently on D:\, but on C:\? No way, I don't want any games (really) going there, I want it to just be critical system functions and core programs only.

So here's the question: do I
a) uninstall Steam and reinstall it to D:\? or can I
b) drag 'n' drop stuff to D:\?

I think the answer's A, but in that case, do I:
a) encounter no troubles, or
b) discover I've sort of fucked up because now the computer's going to get confused when it sees conflicting Steam files from the 2nd install vs. the 1st install (assuming a faulty uninstall on Valve's and Microsoft's parts)?

Because I'll just leave Portal (5 GB) where it is and forego installing the other games if it's B to that second question.