Upgrade to Windows Vista or 7. The volume control allows you to set which program can have higher or lower volume over which. In other words, you can listen to Charlie Sheen WINNING and keep Nyan'ing without having to listen to the Nyan
If you mute Nyan Cat while you're Nyanning, then you're not Nyanning at all. you're just keeping the window open. You must hear the Nyan to Nyan.
actually i love nyan-cat.. i listen the 6 hours extended version on youtube once. if my calculation is correct you have been nyaning for 4,279,728,115,783 years i guess you have a time machine.