instability and slowdown when downloading...

I have a modern system [e8400, gigabyte Ga-P35-DS3L, xp home, 4 gigs ram, 640 gig hd, cable modem, evga 8800gts] I built myself. I like to download movies/music/etc. I use the latest version of Ares P2P. It runs fine, finds a port etc., however, if I begin to download multiple streams (~10-15 large(100kb-1400kb - movies) or ~60-70 smaller (3-10kb - music) at once, my computer will crash to a very quick, print filled blue screen (much to quick to even begin to read it - although I will try to take a picture of it), after making a short, awful sounding, quick cycling burst of static through the speakers. I'm not entirely sure, but it may have started after plugging in a Seagate FreeAgent usb hd (I booted the computer with the hd accidentally still plugged in, and it kind of went a little haywire - although this was months ago and I've had no other issues related to this - I don't think I had this crashing problem before the usb hd incident). Does anybody know why this might be happening? The program works fine if I don't try to download a bunch of files at once, but this shouldn't be acting this way. I have a much older system (that uses an older version of Ares) with which I can download as many files at once as I like.

Also, with both systems, just after I begin a dowload, the internet service slows way down even though I haven't reached anywhere near my theoretical download speed limit (10gps). It does depend upon how many streams I start at once, and their size, as to how long the slowdown will last. At some point, even though I may have 8 or 10 downloads still running, it speeds back up to normal. I run ZoneAlarm which gives me a small red light/green light traffic gauge (upload/dowload) and I get the slowdown even if the guage shows plenty of room for more info. I had thought by building a newer, more capable machine I might get around any type of data bottleneck on my machine itself. Any insight on this issue and if there might be a resolution for it would also be welcome. Thanks for your time...