I have a pc that is now a few years old, but still runs pretty well.

Although its main problem is that it is slow to load up games (specifically COD 4)

Its specs are detailed here:
http://bleedingedge.com.au/forum/viewtopic.php?t=2027&sid=fd09441606073364c7af72f40635910f

I dont know what is relevant, but these look it...

- The NEW Intel® Dual Core Technology Intel® Pentium® D Processor 830 with 3.0GHz, 2 x 1MB L2 Cache, 800 MHz FSB
- RAM 1024MB DDR2 - 533 MHz SDRAM
64bit dual channel memory (1 slot free for upgrading)
- NVIDIA® GeForceTM 6700 XL High-end Graphics Card with 128MB PCI Express x 16 Bus Concept at 525MHz

What could I do to the computer (preferably cheap/free) that would speed it up a bit?

Cheers