This one's a tough one, I'm not sure where to go next.

Problem: I get application crashes. Most often it's Firefox, since I use it most often, but I've had the same crash happen with IE, Opera, Word, and Ventrilo. The app will stop responding, I check the task manager and it'll say Not Responding, and the weird thing is that it's always there twice. I'll have one instance of Firefox running and at the time of crash, but never before the crash, Task Manager will show two instances. The same applies for all the other apps that have crashed. Task manager is unable to end the process, it just sits there doing nothing until I manually hit the restart button on my PC. All other applications work just fine after the initial crash (eg: MSN, Ventrilo etc all work while Firefox is sitting there crashed). Also, sometimes my sound (on-board) will cut out for a millisecond but then come back. This occurs during gaming, mp3s, Ventrilo, anything.

Things I've Tried:
Reinstalling all my applications.
Reinstalling XP
Flashing the Mobo with the current BIOS
Newest drivers for all components
playing with voltages in the BIOS

PC Info:
Legit Windows XP Pro SP2 with the most recent updates
Asus P5N32-E Sli 680i Mobo
Intel Core 2 Duo E6750
2x 1GB Corsair DDR2-800 4-4-4-12 RAM
EVGA 8800GTS Superclocked 320MB Video
Antec True Power Trio 650W PSU
Antec Sonata I case
320GB SATA HD
LG SATA DVD RW

I have no idea where to begin with this one. I was counting on it being software but the windows install didn't help I'm not so sure.

Any ideas would be greatly appreciated.

I get the same thing a lot for Firefox your not alone. But I use it becoz its safer then IE. Since I upgraded to IE7 from 6 I have also experienced crashes too. I downloaded the Beta version of Apple Safari browser for my pc and haven't has a crash yet.

Yes but were your crashes something that task manager couldn't end forcing you to hard restart each time?

At times yes it did. I also tried stopping it from the task manager as well. With IE6 I never had as many problems as I do now with IE7 but it is newer so I can't really hold it against Microsoft. I havent had a problem yet though with the Beta version of Apple browser on my pc and right now I am using Mozzila Firefox and seems to be working fine right now.
Oh before I forget be on the look out for a new virus I had to get rid of and was a big headache off my clients computer. Its called the Security Toolbar and installs itself on the browser of IE7