My brother has a 2 yr old Compaq computer running Windows 98. He has
a Speedstream Efficen Networks 4060 USB modem (although he tells me
it's not really a modem and he still has the modem his system came
with installed--but he uses this 4060 to connect to the internet
instead). His ISP is Ameritech Speedpath DSL. His browser is usually
Netscape. He was enjoying fast connections, downloads, and surfing
with no glitches or problems until one day he decided to try IE 5.0
to see the difference between that and Netscape. All of a sudden he
was back to slower dial-up speeds. In the process of trying to regain
DSL speed, he deleted some system files. Ultimately he ended up using
his Compaq-supplied restore disk to reformat his hard drive. (Yes,
I've told him several times about the benefit of Go Back, Second
Chance, etc., but . . .) He then reinstalled all his programs,
including the 4060. He also resumed using Netscape as his browser.
However, the connection speed is still not DSL fast.

What might have happened? What can he do now?
Any help would be appreciated.