You don't need McAfee. You can download free opensource antivirus software from either one of these sites:
ClamWin Free Antivirus - free open source Antivirus for Windows - Home
AVG Free Advisor - Free antivirus and anti-spyware downloads
And, you can get free spyware software from these sites:
The home of Spybot-S&D!
Ad-Aware @ Lavasoft - The Original Anti-Spyware Company - Lavasoft
As for a warranty, I don't have any advice, but I can give you my experience. I have a Dell laptop which I bought 3+ years ago. I originally purchased the 2 year warranty. Since then, I've extended it 2 more years. When it expires next year, I'll probably extend it for the last year. (They only allow you to have a max 5 yr warranty.) Why have I been extending it? B/c things keep breaking. Due to a design flaw, I've had one part replaced at least 8 times already. They took my specific model off the market only a few short months after I bought it. I've had to have the CD rom drive replaced just months after buying it. I've had the keyboard replaced, the powercord replaced and the harddrive replaced. If I remember correctly, that is it. But, I'm about to get my mouse touchpad replaced because it has stopped responding.
I treat my laptop very well. It's just that Dell doesn't provide the highest quality product. I'm not sure about the desktops, but this is my experience with the laptop.
That being said, their customer service has been great. They've never hesitated to replace the parts.
One last thing...my sister has a dell and her wireless card stopped worked approx. 2 months after she bought it. She had the mail in warranty and we had to send her laptop back via DHL. Well, DHL lost it. It took over a month to get a replacement. But, the replacement was a MUCH better computer. More memory, bigger hard drive, better CD-ROM drive, etc.