What version of Java are you using? Remove your old version & update using the offline installer here
http://www.java.com/en/download/manual.jsp

Also follow the advice here
http://www.gnutellaforums.com/showth...es+downloading

You could also try disabling ultrapeer capabilities (tools > options > speed) & reducing the number of simultaneous downloads... cut it back to just a couple & see how it goes
Do you have more files downloading through the night than when you're at the computer during the day?