Flipping viruses

So, for those of you who have an email address in my contact list you will have received at least one dodgy looking email from us. Get this for a scenario

- We have 4 emails in our sent folder sent to EVERYONE.
- The email that was forwarded out was not in our Inbox or our Spam folder.
- We've run virus software and Ad-aware/Spybot and it found nothing really bad

I changed our password but my fear is there's a key tracker on one of the PCs and we don't know which one.

Any ideas on what to do next?

Needless to say I'm watching all bank accounts and credit cards like a hawk!