I know this thread is old but I've dealt with this card so much, and have seen so many people with no solution around the Internet, that I thought I'd post what worked for me.
My setup: Windows 7 32bit on a Dell Motherboard with Realtek onboard sound and Realtek HDMI sound chipset on an ATI Graphics card. Realtek does not like to compete with itself so this was part of my problem. Every time I would update my sound drivers, my wirless card would get uninstalled and visa versa. I will watch for this in the future when buying products.
First uninstall the card from device manager and make sure to delete the driver files too (the check box.) Keep refreshing the device manager window and uinstalling until it no longer says linksys or Ralink -- just Unknown Network Controller. Do this in the other PCI slot too, if you had it installed there before (see below.) Then remove it from your computer.
Second Windows was not happy when I switched the card to a different PCI slot without completely removing any traces of the old installation first. It kept giving me an error similar to, The hardware device already exists. To solve it I had to go into the registry and search for "linksys" and "ralink" and delete any reference to it under controlSet, conrolSet001, and controlSet002.
Next, I had to completely remove GAC references to it under Windows\assembly. The public key token is b77a5c561934e089. Do a Windows Explorer Search for that number and delete all of the folders. (Don't worry, they'll be back!) I think I got rid of the ones in winsxs too but it's not mandetory.
Do a hard boot by shutting down, unplugging from the wall, and holding the power button for 30 seconds or so. Reinsert the card and boot up.
Now install the driver I've attached. Use the hardware installation wizard. I wouldn't recommend installing the network utility. Never worked for me. This 2005 driver which I got from Ralink or Linksys is the only one that has worked solidly for me. But remember my system is 32 bit!
If this doesn't work you can try going through the registry again and deleting ALL references to linksys that you are sure are not for current device. Then try again with this or another 64bit driver that has this hardware Id listed in the .inf file.
Too much trouble? Yep! I went ahead and bought an excellent $20 TP-link adapter... and now my WMP54G works of course.
Guess I'll setup a wireless Lan.