help with wireless b/band

I have VIRGIN wireless broadband with a Huwai e220 modem. It is connected to
my Windows Vista Ultimate desktop PC via USB. I also have a small network
comprising 1 x Linux Mandriva PC, 1 x Linux Mint PC, and an old desktop
without g/card, monitor, mouse or k/board that I use to store files.
My problem is that whenever I connect to the internet I lose my network.
When I try to change the settings in the "network and sharing centre" i can
get my network but no internet!
I hav etried every possible combination of settings that i can do without
being able to have both.
The strange ting is that sometimes when I connect it all works for about 3
minutes then it falls over!
I have no hair left! can someone please help me?
Greg

Greg