I just solved a problem that has plagued me for over a week with connectivity with this adapter in Vista. First of all, I could not get a reliable connection until I installed the latest Intel drivers Date 3/4/2009 Version 220.127.116.11. Before that Vista would crash occasionally when changing the adapter parameters and my problems were not consistent, therefore difficult to diagnose. I found the Vista drivers very buggy until this version, so this must still be a work in progress for Intel.
After I installed the latestest drivers I found that with my Linksys WRT54GL access point running Tomatoe firmware that I could not get an 802.11 G connection. B connections worked fine. G connections produced failures in the event log that read Security and Authentication: Fail and Helper Class: Layer2 Security Pre-Association and association status: Success Security connect status: Fail 0x0003800b when using WPA2/AES.
The solution is to disable Turbo or Afterburner mode on the router. Turbo mode is only supposed to work with certain Linksys or Cisco adapters and should not affect an Intel card. It should simply fall back to 'normal' mode just like my Intel 2200BG card does with no problems. But the 3945ABG must have a bug in it where it fails to fall back to normal mode and fails security even though is associates successfully.