Welcome to the forum, by the way.

I think XP Media Center SP3 is OK, but I'm not 100% sure.
Your CPU & memory should also be fine. Since you are using Antivirus now, you can upgrade to BD Antivirus Pro 2011 and use your current license.
The direct download link here will download the full installation program: http://download.bitdefender.com/windows/de...us_2011_32b.exe
You will also find good upgrade information in this pinned topic: http://forum.bitdefender.com/index.php?showtopic=20941
Let us know if you have any more questions.
Regards,
I ran into a couple of problems..
The new software installed without a hitch but it is unable to download the update. Each time I try, it comes up with a message in red that reads, Can not connect to the proxy or server..
I click finish and it closes and another window pops up telling me that the antivirus software had a critical error and needs to restart.
I click finish and it sends a report and restarts the program.
I've done this 5 times... After the 2nd time, I repaired it using the repair utility built into the program, but it didn't help. 3 more attempts to update the software failed.
I went ahead and let it run a full system scan thinking that maybe it needed to do that before it could update but it didn't help.
I uninstalled and reinstalled the software and nothing improved. It still can't update and I still get a critical error each time I try to update and on top of everything else I'm now getting random BSOD's..