Do your MP3 songs skip on a standalone player or on your computer?
If it is on a player such as an iPod what model is it?
Do you create your own MP3 files or are these downloaded, If so from where?
Let us know
Could you press CTRL+ALT+DEL and click the processes tab, Then click the show Processes from all users box in the bottom left.
Let me know how many processes it shows running.
Also which player software are you using?
First of all could you use this guide from netsquirrel to turn off anything you can from startup http://www.netsquirrel.com/msconfig/msconfig_xp.html
Once you have done that could you tell me what antivirus you use.
After using the MSconfig guide how many processes do you have running?
Let me know how many processes it shows running now.
Coul dyou download and run ccleaner to cleanu all of your temp files and garbage files from here http://www.filehippo.com/download_ccleaner/
Once you have done that could you reboot and try your music again.