I don't know if a tool exists for Windows (all versions), so in case not, these are things you can try.
Since OP is on XP (and I don't think this works after XP), there is a tool in
c:\windows\system32\ folder called
clipbrd.exe which can show you.
Many people experience such issues due to either Skype, or the IE/Firefox/Chrome plugin for Skype. Try removing them both and see if the issue persists (or not).
Some people experience this when Outlook is open. Just restarting Outlook can resolve the issue.
Although the OP is on XP, some users on W7 experience this when the Snipping Tool is in use.
It also occurs whilst using RDP so close that down.
Lastly, it is because something else is monitoring the clipboard process, but this would typically be tools you've installed so you either know of them, or your IT department does.