Talldude, you have a virus! Probably obtained from downloading a 'legal' music file from LimeWire's P2P network. Popups are not part of LimeWire's program.
I can't remember what name is goes by (researching)...but vigilante groups have been deploying viruses across P2P networks, which, upon the attempt to download music files from over a P2P network, will automatically create a popup of an online music retailer, offering that song to buy over the Internet. It was deployed as a detterent.
LimeWire is well known for it being free of malware. You shouldn't be getting popups.
I wouldn't use Kazaa or Morpheus. They also contain spyware and adware.