Glitchy/fuzzy problems when recording on my laptop?

I have an HP SD MS MMC XD that I use to record my music. Record through an E-MU 0404 usb audio/midi interface and I use programs like Sonar, Reason, Fruity loops, etc.

Whenever I add over 4 or 5 tracks to Sonar or Reason or if i have over three ish audio effects, the computer starts getting glitchy and fuzzy and stops playing, and in Sonar i get that thing called dropout. Also, when i play live i like to use drum tracks from reason or just play back up wav files with windows media player, and many times the laptop has glitched out and stopped playing on me.

Is there anything i can do to stop this from happening? everybody tells me its something to do with my sound card, but i thought everything ran through my external sound card which is my E-MU interface.

also i was wondering if anyone knew of a liable recording/live performance computer under or in the price range of $500?