PC Security, AV, AntiSpyware, Firewall, Suite

Build your own security suite for free:
Clearing doubts:
1. Many security companies use the same signature base for paid as well as free version. Paid version may have some more feaures.
2. Two antivirus may not conflict always, if they are compatible and light on PC resourse.
Make suite:
Use AVG 8.0 free version for base antivirus. Light on system resourse. Anti spyware also.
AVG does not detect a rootkit if already entered in the PC.
Use ThreatFire 4.0 in association with AVG. ThreatFire removes already entered rootkit also. Also has behavioural analysis and identify Trojan Horse based on that.
Use OnLine Armor 3.0 as a Firewall. Limit on XP firewall- only prevent incoming connection. Vista prevents out connection also but not ON by default. Be sure to turn off Windows firewall. Both can not work together.
Use Super Antispyware 4.25 - Acts as a supplement to antispyware of AVG. Handles stubborn spyware and adware.

Alternatevely, a free all in one security suite is COMODO Internet Security. This does not include antispyware.
If you are a little bit techy, you shoud use the combination of all 4 components.