if you insist on using winamp, just go and download the winamp lite version, just a basic player, i'm using a higher spec pc than your office pc, and trust me, when i tried using winamp 5.05 my pc lags too when it's changing songs, crap, problems solved with the winamp lite
AND, i'd think your pc is clogged up with too many applications eventhough you don't use the applications at that time, right? what's best is, change all the settings such that programs DON'T load at all when u startup PC, most of the programs have this options
next, ensure under Start.. Programs.. Startup ... there's nothing in the Startup folder, if there's anything, just delete them, it won't affect the programs, those are just shortcut links..
you can check what softwares have been loaded by just pressing Ctrl-Alt-Del, and check the Task Manager
finally if you're still stuck with some programs that couldn't be 'switched off' no matter where u search ... (don't attempt if you're not really sure)
go to Start, Run.. type in 'regedit' Enter
go to Hkey_local_machine, Software, Microsoft, Windows, Current Version, RunServices
at Runservices, delete those entries that refer to certain programs like MSN, Realschedule.. etc.. if in doubt, then just leave them alone
note that softwares like Norton Anti Virus, or external firewall programs, sucks up resources big time, u might want to stop these programs from starting up
after you're done with all the 'switching off', if all above permits, you SHOULD only have these 2 things left in the Task Manager,
1. Explorer
2. System
it might be helpful also if u try Defragmenting your harddisk, update all the drivers and updates for hardwares and softwares respectively
good luck in tinkering with the pc !!
PM me if u need help