My network wireless adapter keeps dropping off

I have a hp pavilion tx1000 tablet notebook. I have been having a problem for some time since I upgraded to Vista Ultimate where my wireless adapter, broadcom 802.11a/b/g W/Lan, keeps dropping out of the network adapter list. The real problem is that it is not consistently happening but every time I boot up I don't know whether I am going to have wireless internet access or not. At the moment I am using a mobile broadband solution to connect to the net and that is too slow and limited in download/upload per month to 2 gb.

Please help, rgs Vince