Your system should run it just fine without a CTD, but 2.1 seems a bit underpowered. I'm running an i5 2.81 quadcore with 4GB of DDR3 matched RAM, and a Zotac 8800GT 1GB graphics card. No CTDs here. Going to upgrade to an i7 soon for more power,along with a newr graphics card..... as soon as I can afford them.
There is a 4 GB patch that will up your memory useage to 3.7. Get that and see what happens. Know too that XP will never use more than 4GB of RAM. The only way you can is with Windows 7, and I believe that will let you used up to 16GB.
What size power supply do you have? A 750watt is about the lowest size to use with the hardware you have. 2 graphics cards could be the drain on yours making the SH5 crash.
Also your processor cooling might cause it. I've been running a Corsair H-50 water cooling setup, and it works a lot better than just a fan.
And make sure you keep the inside of you case and hardware clean. Dust and all that other crud getting sucked in will cause problems too.... even major problems more sooner than later.