Protection for your PC ??

Virus Detection : I use all of the main ones available for testing purposes but I prefer Norton over the others hands down.
Privacy: Spybot and AdAware. But I rarely use them and usually just do the removals manually.
Data back-up: 20 GB MP3 player, hundreds of CD-Rs and several remote servers.

I also back up data on 4 different computers in two locations as an additional precaution.

You can encrypt all the data on your computer on some OS's, though it does not solve everything of course.

Virus protection: Norton. I also use Stinger to remove specific threats. AVG FreeScan is crap (the few times I've tried to use it on someone's system it didn't remove any viruses they had) but it is the best free option out there
Adware/scumware removal: Spybot. If it doesn't remove something I'll fix it manually
Backup: I copy data to a 2nd partition, and to USB thumbdrives and CD-R's every now & again

Virus Detection : AVG Anti-Virus full version (switched to this from Norton).
Spyware: Spybot Search and Destroy
Adware: Pest Patrol
Data back-up: About once a week. If I take digital pictures or videos, I back-up them up right away.

Linux.

going to put in something for ads soon soon as I free up a computer

AV: E-trust, got this freebie from a partnership of MS and CA, an award-winning AV engine (actually two of them) and updates for a year (reg. $50). If you don't have AV yet, or you're running a real freebie like free AVG, get this one, the deal is good through June I believe. We use the corporate version at work, and this is the only program only charges for program updates, not definition updates, so you can keep getting new defs after your year is up, you just can't update the engine or program.
Spyware/Adware: Spybot. I just don't install adware filled stuff anymore. There's always a way to find truly free stuff that doesn't have Adware. I just use Spybot to keep the cookies down.
Data backup: none of my data is important enough that I can't live without it. Though I do have two HD's now and may begin some form of rudimentary backup.