Maybe things have changed but neither Spybot Search and Destroy not Ad-Aware used to have antivirus and I have always used both as well as whatever antivirus I ran - with no conflict issues. I used to love Tiny Personal Firewall too but it seems there is no current version.

The only AV that ever let me down was Avast, but it was perhaps the least of a resource hog. Norton simply slowed everything down to a crawl and refused to co-operate with any dialup email until I turned off scanning outgoing mail. Panda was OK. I haven't used McAfee since the first time I installed Win 98.

I find Win Essentials OK.