When in doubt, I can say as a person who has worked networking/security, pull the network connection. No connection, no data going out. Can save you lotsa trouble if you have indeed been attacked. Hack victims have become unknowing storage places for files, typically music, movies, and wareZ, so you can look for mysterious files in odd places (like the recycle bin, for example- win search doesn't check there, but from the dos prompt you might find it..)
ZoneAlarm is a decent program for detecting incoming/outgoing packets that you don't want moving around, but at the same time the program frequently flags legitimate traffic. It's a worthy extra measure if you need it. Just double check anything it reports and be sure you know what exactly those odd packets are.
If push really comes to shove: Reinstall your OS of choice. Immediately, before reinstalling any other applications, run windows update. Install all the apps you are going to install, run update again. Especially if Office is part of the collection. Install the firewall software/zone alarm/etc before running win update again. Check the vendors of each software that you've installed for updates. Run winupdate again as the last measure after finally installing everything, hopefully there are no updates.
Hope this helps some.
