In my opinion, all Internet Security Suites are resource hogs. Most people get sucked into thinking if you pay, your 100% protected - your not. No program is foolproof - there is no argument with that. Malware changes constantly and the database signatures need to be updated for these new viruses - that is, once those new viruses are found.
However, when you pay, your get technical assistance.
But, if you want to take some good advice, I would recommend the following:
AVG Anti-Virus 8 - Includes Anti-Virus and Anti-Spyware all in one.
COMODO Firewall PRO - Great firewall and includes a Defense + feature which no other firewall (pay firewall) has (to my knowledge anyway).
SpywareBlaster - Use this to help protect your from malware. Sets a list of potentially hazardous sites, cookies and ActiveX controls.
If you want to go even further, have a go at using an alternate web browser to Internet Explorer - Mozilla Firefox is one that comes to mind
Well I hope all this didn't overwhelm you and it made a difference