Its wise to be asking this question, i still know of quite a few people who do not have a single anti-malware product on there system,and refuse to have one because,and i quote: "it's not made by microsoft,so i dont trust it"
,oh the arguments ive had with them and some are learning the hard way now.
Well, there are alot of great free pieces of software out there. Its probabaly a good idea to have about three to four pieces of anti-spyware/malware products on your system,you dont really need more than that. A good firewall is needed,not the free one built in to XP,but a proper firewall that works effectively.And,just one
anti-virus software,more than one and they will conflict letting things into the system.
Some great pieces of anti-malware software you might consider are:
Ewido (which from another post of yours,i see you have already)
Windows Defender (still in the beta stage, can be dodgy on occassions, but still not a bad kit to have)
SpywareBlaster (not an actual running programme,this adds sites to your blocked sites section in your browser,preventing you from opening pages that are infected.Just remember to keep it updated)
SyGate 5.6 (I use this one,its no longer supported but still very powerful)
and i hope you already have an anti-virus product but if not,try one of these:
All of the above are totally free,and extremely effective products, it just comes down to personal taste, but id personally recommend Spybot,Adaware SE and Ewido as your main three then whatever else you choose to add and also download SpywareBlaster.
If you look around on the forums,there are lots of recommended freeware products.