Stupidly slow wireless connection

My wireless connection is ridiculously slow.

Up until recentley it was dead fast. Then I got a new USB broadband modem
and reset up the network and it suddenly became slow. It was running
consistantly at 54 mbs now it is running at 1 mbs.

I set up the network using the network setup wizard on both machines
(windows xp). I did the default option most things. Is it possible that
there is some advanced setting I need to change?

For the record, I have an adhoc network between a desktop computer and a
laptop. The laptop has a belkin 54g wireless PCMIA card and the desktop has
a NETGEAR 54g wireless PCI card. The modem is a ZOOM ADSL external USB
modem.