To answer the "Do I need several different programs" bit of your question:
A full security suite has 3 essential elements. They are as follows:
Firstly you need a decent Firewall. Windows (from XP onwards) has its own built-in firewall but it's generally regarded as less than perfect. The most popular free alternative is Zone Alarm Free Edition, with Comodo also having plenty of fans.
Secondly you need anti-virus software. The free version of AVG is the most popular, but Avast! also receives plenty of praise, as does Avira AntiVir.
It's important to only have ONE firewall and ONE anti-virus program running on your PC, otherwise software conflicts might occur. (Zone Alarm automatically switches off the Windows firewall when you install it. Comodo probably does the same). However when it comes to final link in your security chain (which is anti-malware software) you can have as many programs as you like. (They only run 'on demand', rather than 'in the background', so conflicts won't occur). The most popular free programs are Ad-Aware and Spybot Search & Destroy, with the free version of Malwarebyte's AntiMalware also widely praised.
Chris