Ok. You can begin with antivirus. You can use AVG free, Kaspersky Free, or PC Tools Free antivirus. They're all recommended by Kim Komando, a techie with her own website. www.komando.com.
Then for antispyware programs. I personally use AVG Antispyware, Spybot S&D (Search & Destroy), Ad-aware SE Personal and, Superantispyware. You can get all of these, except Superantispyware, from www.komando.com and this website. Superantispyware you get from www.superantispyware.com.
Last, but not least, a good Firewall. You can find a free one on this website. There are a few. I use Zonealarm from zonelabs. It takes a little getting used to telling it which sites are ok and which aren't, but once you get used to it, it's really good.
How do I know all of this? I have all of these on my own computer, and, when I work on someone elses, and they don't want to spend a fortune on software either, I install them on theirs.
I totally agree with you regarding Norton. That software is a space hog, and, it also causes your memory chips to heat up too much, which, wears them out faster.
Hope this helps.