I was having some of the same problems with Build 5 that have been reported here, but after I uninstalled Norton 360 v.2, I did get PT running. (I haven't tried the HUD yet, so I don't know one way or the other about that.) And PT also will open for me with the free version of avast! going.
However, I'm encountering problems whenever I try to open PT with a firewall running. The Vista firewall doesn't seem to create any problems (but I've also heard its not very good). But when I've tried opening PT with either the free version of Online Armor or the free version of Zone Alarm, the following happens: I get asked by the firewall to grant access to PokerTracker, and I give permission. At about the same time, I get a "welcome to PT" announcement that tells me where I can get more information. When I click "OK" on this announcement, the PT3 logo does not appear on my screen (I mention this because it DOES appear when I don't have a firewall going), and then the program does its disappearing act -- it doesn't start up, but whenever I click on the desktop icon for PT3, I get a message that it's already running.
And I may be giving some unnecessary detail while also leaving out some important information, but the problem is, I don't know what I'm talking about. I'm not very knowledgeable about the technical aspects of computing. Anyway, are others having similar problems, and is there a solution yet? Apparently I can run PT3 as long as I have no firewall going, but I'm nervous about playing online poker on an underprotected computer.