LAN/speed problem

I'm on a two-PC setup. The laptop has the modem, and this desktop is connected to, and accesses the net through, the lappy. Problem is: I'm getting download speeds of 10-15kbps with HTML dls. BT is largely fine--my speed's governed by seedcount, etc. and P2P dls don't suffer either, but for HTML dls: almost constantly a 12kbps average.

I've had this problem for a while but it's only recently got on my nerves. I use Firefox 1.5 if that's useful information.

Thanks for any help.