unable to download anything

Just recently my neighbor has been unable to download anything off of the internet. He can browse web pages perfectly, run all java applets, and everything else except download files. Even when we try to use windows update it just hangs and eventually stops responding. He has DSL so not being able to download anything kinda sux. We got one download to start once but it was going at 110Bps, 14.4k dialup would probably go faster. The strangest thing is that he is able to get his e-mail and everything but no downloads will run at all, not even kazaa. we have already tried reinstalling xp several times, installing xp sp1, playing with network connections, and other things. I believe this problem started when he set up his home network but it may have been some time after. Today I am going to try taking his computer off of the network and taking all of the sharing off. Other than that I have no ideas at all. If it comes to it I will have him back up everything and reformat.
Norton systemworks 2003 finds a missing or currupt dotnetinstaller.exe and is unable to repair it. I thought reinstalling xp would have fixed that but it didn't.
the path is:
c:\program files\common files\installshield\professional\(a folder i don't remember but it was the only one there)\(a folder i don't remember but it was the only one there)\dotnetinstaller.exe

His computer:
PIII 733
512mb pc133
40gb IBM
gf3 ti500
2 10/100 ethernet cards, one kensington, one netgear
Windows XP Pro

Other comp in network:
Celeron 700
128mb pc133
4.7gb WD
ATI rage 128
integrated netgear 10/100
Windows Me

other:
a netgear 4port hub
speedstream 5260 DSL modem
SBC DSL

If anyone knows what it is or has any suggestions plz tell me!! My neighbor really wants to be able to download things again.