There's one thing I can suggest straight away. You say you are running XP Pro SP2 with only 256Mb RAM. Try upgrading that to at least 512Mb, and if you use the computer for games and graphics programmes like Adobe Photoshop, you'd be better off with nearer 1Gb.
It could also be a heat problem, as it only shows up you say when you use your MP3 player. There are many other things it could be, like a power supply that's needing to be upgraded (a lot of them are the ones supplied by the maker, and are only capable of 250 Watts in most instances) you may need to upgrade to a 350 or even a 450 Watt model, dust on your CPU fan and in the CPU heatsink slots - as I said, many things. One good thing, if it's just heat, try running the machine with the side cover off for a while and see if the performance gets better, if it does, check out the CPU fan and heatsink; AND get more RAM.
My problem is when I click on a page, it will jam and have a sound 'cick...', then I have to move my mouse around quickly, then it will be fine and go to the next page. But some time when I click again, it will hang down there on that page, so I have to shut down my computer. I have reformat my hard disk but still the problem still come again. I found out that my CPU Usage sometime always went up to 100% when I play my MP3 and check my e-mail, then my music starts to 'jam jam jam...' every thing goes very slow and sometimes Hang. Can someone pls give me some advice on this Computer Hang problems? Thanks!
P.S. My PC is running on WINDOWS XP PRO SP-2 Intel Pentium 4 CPU 1.60GHz, 256MB of RAM.