Yep it's the processor. Not much you can do about that without getting a new video card or a new processor.
Q2 uses as many CPU cycles as it can by default. I am pretty sure DP does, also (cl_sleep can reduce this). 100% usage is not indicative of a poor CPU.
KI3S, hopefully DirectX is installed. Go to start>run>"cmd" and enter "dxdiag". You can then click the "save all information" button to save a .txt that you can upload. This will contain system specs, including video card specs.
I don't think it's possible to determine your problem in this thread if it involves freezing. The best generic advice is "reinstall windows", and if it keeping happening, you should suspect a hardware problem (overheating of the CPU is suspect).
To see if it's just hardware related, you can try 3D overclocking utilities like ATITool, which can be used to put the card through a stress test (ATITool just displays a furry rotating cube which gets my card really hot). If your system freezes, then your video chipset is probably overheating.
You can max out the CPU with something other than DP using prime95. If it crashes, you can be sure you have a processor heating problem.