Recently on Call of Duty: Black Ops my FPS has been extremely low and I have been getting spikes.

I set all the graphics setting to minimum and found that I would get FPS between 80 and 100, but when I began to shoot it would drop down to around 25 and my screen will often freeze for a second or two.

Here are some specs:

OS: Vista
Processor: Intel(R) Core(TM)2 Duo CPU T9800 @ 2.93GHz (2 CPUs), ~2.9GHz
Card name: NVIDIA GeForce GTX 260M
Current Display Mode: 1440 x 900 (32 bit) (60Hz)

(Annoyed that for whatever reason, I couldn't add attachments to this thread)

If you need more particular specs then just ask, since as you can probably tell I'm not brilliant with computers (Please excuse my ignorance!)