I'm running on Windows 7 32 bits. It was working perfectly normal on ultra settigns before the patch:
GPU-Radeon HD 4830
CPU-Intel Core 2 Duo E8500
Probably Win7 32-bit at the minimum being the main culprit for the crashes. The other two are pushing it and borderline insufficient as well for the HD pack, especially if there's only 512MB on that 4830.
The biggest issue is the patch increased texture size from ~1.3GB in total to ~3.2GB, some of which are shared, so its probably closer to 3.5GB with HD textures. Without getting super technical, if you can get access to a copy of Win7 x64, your 32-bit key should work with it. I'd start by reinstalling and upgrading to x64 and see if it fixes your crashing problem. You still may get poor performance and stuttery/hitching with the HD pack, but at least you won't be crashing every time you try to load a new zone.