Be VERY sure to remove Norton first (via control panel -> add/remove programs) and then reboot the pc in the normal way. After that point, you'll be able to install a new product. Failure to remove first and reboot, will often result in a disaster. Norton can be almost as bad as a virus, if not removed properly
AVG PROFESSIONAL MALWARE EDITION is the one I have been using these days, and it hasn't let me down yet. The price is right, too.
AVG anti malware can be bought online at
www.grisoft.com with a 12 or 24 month license. Most shops have at least a couple pc's at the front counter(s), a CMC in the back, maybe even a public use printsearch or artaissance pc for customers. (or a pc at home that needs protection) It's cheaper to buy the licenses in bulk:
A 1 computer, 24 month license is $44.95 ($22.48 yearly)
A 2 computer, 24 month license is $81.95 ($20.49 yearly, per pc)
A 3 computer, 24 month license is $101.95 ($17.00 yearly, per pc)
A 5 computer, 24 month license is $146.95
($14.70 yearly, per pc)
Note: all pc's on the license contract will expire on the same date.
AVAST is another great product, with similar pricing.
http://www.avast.com/eng/avast_4_professional.html
Both products have free (for residential use only) versions, and full (pro version) trial periods. The pro version has more options, and scans can be scheduled to run once per week instead of every day.
Good luck
Mike
PS: Don't forget to participate in this year's Frame Shop Technology survey, which asks about this very topic. It's in the main forum.