Damn, this sucks, another one.
I too had Win 7 without SP1 on there.
I'm wondering, were you also running RDP or VNC services? VNC for example could've been cracked if you had an easy to guess password.
Try running a bunch of online virus scaners like bitdefender, f-secure online scan, eset online scan, panda activescan...
Run spybot, malwarebytes..and last but not least combofix in case you may have a rootkit. Either way dude I strongly recommend you format, reinstall get yourself a legit copy of Win 7 if you don't already have it and update to SP1. Also if you are inclined to learn a bit about linux setup a dedicated linux box to store your bitcoins on. At the very least run a Linux install in Vmware or something.
If it is a targeted bitcoins virus, it would just loads up your wallet and sends the info via a web call. Your firewall wouldn't even stop a gets. It is really unlikely that any virus programs are going to catch something that simple, antivirus software hasn't yet learned that anything accessing wallet.dat is probablt bad. Of course, since no one should be stupid enough to run such a program, it is possible that it got injected through some known exploit. In that case, antivirus should find it.
http://k.min.us/ikZZRk.zip (Namecoin binary build) <-- this is the only thing not open source/from trused place. But its namecoin and the link is in this forum.
Things on the forum are the most suspicious, since the forum is the best way to get malicious software out. If I had to guess, I would start there. I would hate to see someone use namecoin this way, but you never know.
EDIT: I can't find that link anywhere on the forum. Where did you find it?