Just my opinion here.
1. A current antivirus. Some don't have such or let them lapse.
2. XP? You need a firewall. If you have SP2, then it's enabled by default and stops the usual worms.
3. PEST CONTROL!!! An Anti-Parasite Suite such as Adaware, Spybot, Stinger and Housecall. Cwshredder is not being developed but may help. Keep reading in the Security Forum for updates.
4. Try another browser. Internet Explorer has some issues...
I have worked with laptops for almost a decade, but always on a company machine that was administered and maintained by the company's IT group. I have recently purchased my first, personally owned laptop - a Dell Inspiron 8600/1.6 Ghz/512MB/40GB/XP Pro - and I suddenly realize I don't have the know how to keep it running smoothly and to "monkey" with it to diagnose any issues (I hear Dell isn't the most useful first line of defense). Can people suggest either a single book or website they consider a general "must read" for the newbie? Thanks.