You've done the usual so it sounds like the usual failing wifi card. Yes it works in safe mode which proves little except repeating the same story I've heard too many times. We nod and listen and fit a wifi pc-card and it works again. Then the owner wants the internal wifi fixed. We've been there, done that and know to never do that as the owner will only come back next year when the internal has failed again.
One last idea. Change the wifi channel on the router. Be sure you are not hiding the SSID and the security is WPA.
I have a Dell XPS M1330, since I moved to my new house, the wireless barely works on it, my housemates report no problems, so I guess it's something to do with my laptop. It's eratic in normal mode, sometimes not working for days, usually working on-and-off, forcing me to reload pages a few times before they work, etc. It works perfectly in safe mode, the driver I'm using is the Intel PRO/Wireless 3945ABG Network Connection, version 18.104.22.168, with a date at 26/10/2009, the most recent one I could find, bluetooth is not enabled, and I'm running Vista 32-bit Home Premium, which it shipped with.
I also tried disabling IPv6 and resetting the IP stack, both to no avail. Can anybody help me?