I just bought a new PC and upgraded to the Total Security 2008 version.
I had previously experienced Norton / Semantec and was totally dissappointed with it dramatically slowing down my PC. Their technical response was slow, confusing, long-winded and very expensive. After consulting our IT Dept at work I bought BitDefender a year ago and haven't looked back since.
Total Security 2008 loaded easily and performs well. I like the facility to periodically clear out rubbish from the computer registry which can speed up the PC and keep it responding quickly. I also like the facility to regularly and automatically back up my files and photo collection.
I notice that its specification states it needs a CPU chip clock speed of 800MHz or higher. If that's an indication of the security software industry standard it's worth bearing in mind when buying a new PC or laptop. Luckily my new PC is 800MHz. Email response from BitDefender has been very prompt and comfortingly personal.
You can download a FREE evaluation version for for a month from their website (bitdefender.com) but I found its best to actually buy any security product on a CD (from Amazon) as opposed to downloading it. That way you have a CD to keep and a properly bound user's guide.