Norton 2005 crashed my PC aswell, succeeded in getting it back up working the first time (by entering safe mode and manually removing most of the Norton folder). Thought it crashed it because I wasn't connected to the internet at the moment and thus the auto updater would cause trouble. This was wrong as I noticed later when it pretty much totally wrecked windows (system restore didn't work, nor safe mode).
I use, what feel like a very powerfull anti-virus now, Avast Antivirus. this is the link:
http://www.avast.com/.It is free to use for everyone but not for companies, also there is a pro version I believe with a cost to it. The program has, since I installed it after a fresh XP install two weeks ago updated it self a up to a few times a day. It's also discovered viruses and removed them aswell as discovered viruses in my mail box (using Opera mail). It is scanning the computer at all times unless you terminate it. I haven't noticed a whole lot performance drop but I do usually turn it of if I know I might have big fights in AH. I like it alot, it has already saved my computer more then 10 times in just two weeks.
Together with this I use Microsofts AntiSpyware (Beta) which is also free. This is a fairly new (I believe as it is in Beta still) anti Spyware program, it also autoupdates and checks your system registry every time a program tries to add anything there, you have the option to accept or decline based on the info you get. Every step you make you can send in to Microsoft spyware network. This network consists of pretty much everybody who use Microsoft Antispyware, if one user finds spyware he reports it and as far as I've understood, it is added to the spyware database and also verified by pro's.
This too has saved my computer a few times already and it works a hell of alot better then Adaware or any other spyware program I've tried.
Both highly recomended.