Vista - Switching User Profiles Inhibits My Internet Connection Speed

I am using Windows Vista Home Premium with 2 users, Mine (Admin) and a second
one (Standard User). I have a DSL Internet connection that was working just
fine on my XP computer (same setup), but with Vista (brand new and completely
different computer), it will only work for the first User Profile.

It doesn't matter which User Profile I load up first...If I try to switch to
the other User Profile, the Internet Connection is severely constrained. For
example, normally it takes only a fraction of a second to download a simple
text email or load a simple webpage, but after I have switched to the other
User Profile, it takes minutes to work, if it works at all. This is the same
if I log off of one User Profile, then log into the other User Profile.

I have tried this with and without my router and the router does not seem to
make any difference.

Any help??