what security software should i get ?

Can some people with experience here advise me as to what security
suite software (antivirus, firewall, antispam) to get for MS Windows
XP? (free or commercial, but I am suspicious generally of free
software for MS-Windows that often has viruses and annoying popup
malware associated with it)

To be honest, I have been using Ubuntu Linux for quite some time, on
dual boot systems (WinXP and Linux). I find myself increasingly in
need of only MS-Windows for the software I need to run (Sony Vegas,
Sony ACID Pro, Movie Magic screenwriting software, etc) and may be
just foregoing linux or perhaps taking it off my systems entirely.
Thus my concern for protecting myself from viruses, trojans, etc.
Today I downloaded and am running a trial version of Kaspersky
internet security, just to have something at least for 30 days. But I
am open to any security suite, as long as it does not slow down or jam
up MS-Windows too much.