slow browsing speed

I'm getting real slow internet browsing speed and one connection only
downloads. i dunno if this is MTU problems or not, but when i connect to
nntp servers and use say 4 connections i get over 300kbyte/sec and if i
use up to say 10-16 connections I get around 450kbyte/sec -
490kbyte/sec. when browsing the web pages load slow, speed tests online
also give me poor results usually saying less then 3000kbps or even
worse then 2000kbps. is this MTU related maybe now that i have a 4mb vs
1.5mb or anything in my past? I'm using win xp pro and plenty fast AMD64
3500+ etc gaming machine. i do know my connection is 4mb.