File sharing apps like Limewire can really slow things down for a few reasons:
1. Processor-Open task manager and check the processor utilization. Limewire is probably beating it up pretty bad (Bearshare does the same).
2. Bandwidth-When you are searching for and downloading files, you're really choking your internet pipe. The internet WILL be slow (even with cable).
3. Memory-Always a possibility, but not the first place I would look. Again, look in task manager & on the Performance tab, look at the Total & Available #'s under Physical Memory. Let me know what they say.