Windows vs Custom Security; Opinions Wanted!!!

I just completed my first PC build. Before I connect to the Internet or transfer files from my XP machine to this new Vista machine I want to make sure all my Security is airtight.

I used to have issues with security, virus's, spy, browser take over, etc. on my XP machine I was advised by a Network Engineer to disable everything Microsoft (Windows) and install 3 things.

1.) Ad-Aware SE Personal (Free Download)
2.) Spybot Search and Destroy (Free Download)
3.) Symantec Antivirus Corporate Edition activating Live Update, which updates all definitions non-stop in realtime whenever connected. (Not free or cheap)

I am guessing I can still do a free download of the first 2 and I have the ability to swap the Symantec from one machine to another.

Are the first 2 items on my list still the best things out there at what they do? And does anyone think that Vista Security is better than these three things combined.

By the way my XP machine never had an issue since and for the last 3 years. I am very confident in what I have but open to things out there being better. I don't think I can utilize these if Windows Security is being used, some type of conflict in communicating or how the programs "see" each other. Something like that, way over my head.