Definitely run HiJackThis. It will keep certain spyware from re-routing your IE browser start-up page.
I use Ad-Aware daily.
I also run a little program called WinPatrol. It notifies me if any program tries install an executable. Most executables are legit from newly installed software, but some vial websites and viruses can plan their own .exe on your hard drive. (A couple of years ago I had acquired a virus that hid itself in the recycle bin, of all places; ended up having to reformat the hard drive to get rid of it.)
I have just started running AVG Anti-Virus (free home version). I have been running a Micro-Trend AV but its auto updates run out in a couple of months. I don't know what the cost of the new AV will be. If the free AVG seems to work, I will go with it. (It already found one virus hidden in a zipped file that the Micro-Trend didn't see.)
Do you know if Norton's does the job of WinPatrol? Part of my purpose for posting is to learn about some these more obscure programs (virtually everyone has the programs I do).
House Call from trendmicro is free and their virus definition tables are kept up-to-date. I've never owned or paid for a virus scanner(but I'm vigilant). When I have had virii or worms I just search Google for the removal tool if House Call couldn't quarantine/delete the infected file(s).
Hijackthis is for advanced experts. The average user will get heartburn from it.