Another good free anti-virus program that doesn't seem to have been mentioned is Grisoft AVG. You have to register to get it, but there's no charge. It's regularly updated and has a plugin for Outlook/ Outlook Express, if you're still using that. Whatever tools you use, it's very important to keep them updated, and of course that you run them often!
I use mostly just AVG and ad-aware (also, occasionally, spybot, but it doesn't often find stuff that ad-aware has missed, and it's not updated very often), and it keeps me pretty clean. _Very_ occasionally I'll find that AVG won't run. In those cases I reboot, go immediately into task manager/processes and shutdown any process I don't need to be running that are under my user name. Basically, everything but explorer, then re-run AVG to get rid of whatever was preventing it from running.
I recommend getting rid of Internet Explorer and Outlook Expresss and replacing them. In the past I've used Opera, which works very well. The only caveat is that the free version has a fairly large advert window. I'm currently using Mozilla Firefox, which I can't quite reccomend unless you are tolerant of a few quirks - it's not quite ready for primetime!. All of my kids are now using Mozilla.
For news I use Forte Agent, which isn't free, but I really like it. Waaay better than OE for news. Most of the kids all use web clients for mail, but I just started using Mozilla Thunderbird. It's also quite good at extracting your settings, address book, and stored emails from Outlook Express. The reason I stuck with OE for so long was that I couldn't get anything to import my rather large email archive. Thunderbird did it first time. There are also other good email clients around, notably Eudora. I tried that and liked it, but it couldn't import all of my email archive, so that's something to watch out for if you try it.
Thunderbird also does news, and while it's not good enough to lure me from my already paid for Agent, it might have been good enough to prevent me buying it in the first place, if you see what I mean?