All P2P Progams max my system resources... help!!!

[GreenMunky]

Okay, before I get started here are my system stats:
AMD 64 3400+
1GB RAM
Windows XP Pro.
150 GB HD (100GB Free space)

Every P2P progam that I've tried to use over the past several months has maxed out my system resources and made my computer impossible to use while a file is downloading. I've used Limewire, Azureus (lots of other torrent programs) and everything's fine until I start downloading a file... then as soon as it gets going my computer starts to respond very slowly and if that continues too long (if I pause the download everything goes back to normal) the download speed begins to decrease very quickly and if it gets down to 0kb/s I lose the internet connection completely and I have to restart my computer to re-establish a connection. Does anyone have any idea what could be causing this problem and any possible solutions? I have scanned my computer NUMEROUS times looking for viruses, spyware, malware (PLEASE keep in mind that I do NOT have any anti-virus programs or ANYTHING else running that's taking up the system resources... whatever program I'm using to download is what is taking up 50-100% of the system resources in the task manager)... I've defragged my hard drive, and I even disabled UPnP in both Limewire and Azureus. Please help, I'm desperate. Thank you for your time.