Not sure if you're still waiting for feedback.
When my laptop arrived it had Vista preloaded. My previous router had WPA-PSK (no WPA2) and that just did not work under Vista (only the first day it did work oddly enough ...). That and a couple of other huge annoyances caused me to "downgrade" to XP (I guess the terms upgrade/downgrade are subjective to personal interpretation ).
Obviously you are not in a position to revert back to XP. My best shot would be to use WPA-AES or WPA2. Be sure to check if there is a newer/better driver available for your wireless card. Also try a wireless USB adapter if you have one.
Also, I have noticed that certain network cards fail to connect when you set them to 54G only. Some cards just refuse to work unless you choose B/G Mixed mode ...