If you don't already have them...
Ad-Aware SE Personal:
www.lavasoft.de
SpyBot Search & Destroy v1.3:
http://www.safer-networking.org/en/index.html
Microsoft Malicious Software Removal Tool:
linky
These three used in conjunction with each other will rid your PC of any spyware or malware lurking on your system. You should also have up-to-date anti-virus protection, either paid for or free, whichever you prefer, and make sure that you have some kind of firewall protection, even if it is just Windows Firewall!
I would hope that Ad-Aware and Spybot should tackle any rogue software on your computers, usually does the trick! Here at home I use both applications regularly (scans performed once a week) and also have AVG AntiVirus Free Edition installed and up-to-date. Finally my broadband goes through an ADSL router with built-in firewall, which I have got locked doen tight, and so far... so good
HTH!
EDIT: oh yes, get Firefox too whilst you're at it
www.getfirefox.com