HL2.exe has been stopped Error

[Scuber]

I just recently got myself Team Fortress 2, a few days ago, and i haven't been able to by-pass this problem and now totally out of ideas.
The error message occurs just after the Steam "is preparing to launch..." window dissappears, each time i try to launch the game, from both shortcut and via the Steam app.

[I can post my full system specs. later, if required]

Windows XP Pro [SP3]
I exceed the recommended system requirements, using:
nVidia 7900GT, 3.0GHz Processor, 1.5GB RAM
Avaste Anti-Virus and Ad-aware


In attempt to solve the problem; I've updated my sound card drivers, nVidia drivers, ran a windows update [then realised SP3 was available], redownloaded and reinstalled both the game and steam, disabed my sound card entirely, terminating my anti-virus and performing spy-ware scans, updated my directX to 10 and tried running the game through multiple formats [including windowed, default settings, no video intro etc.] However, having tried to run the game between each interval of upgrading and testing, they all remained to issue me with the same error.

I'm all out of ideas now, I've recently sent a report to the Steam Support team but feel it may be some time before i receive a response and hope that some technical helper might be able to cut me some slack as i'm still yet to even play the game at least once.