I suggest that you use the NIC own application software to connect to your internet gateway (router) I have helped many people who have had this type of problem.
I first had problems with a INPROCOMM WLAN with a SKY Sagem Router it would drop out or go to 1MB connection and sometimes loose the 54g signal all together. After a restart sometimes the laptop would not find the profile and no connection was made.
As soon as I disabled the WZCSVC Windows Service (Wireless Zero Configuration that provides automatic configuration for the 802.11 adapters) as it is designed to search for new routers every 20-30 mins this had to be my problem they appeared to contradict each other.
As soon as I disabled this service all my problems stopped, incidently if you have a Desktop with an Ethernet LAN 100MB connection if this service running is it useless and also takes some processor power even when it is not needed so just use the DISABLE_WZCSVC tweak anyway.