Firstly, a Prism 54g what? USB? PCMCIA? Mini-PCI?
Secondly, don't expect things to go smoothly - or indeed work at all - with Vista Beta. Particularly with less popular brands such as Prism, which will likely take longer to produce suitable drivers.
Thirdly, if there is no update on Prism's support website yet (assuming that it has one) then it's a no-go for now.