1. Make "doubly" sure that it's the right driver (vista 32bit). Sometimes I swear I got the right driver, only to find that I didn't.
2. Make sure that you updated your PXE server after you inserted the drivers. Either redeploy PXE or update your WinPE image using the script here: http://community.landesk.com/support/docs/DOC-7619 . Do you have multiple PXE servers? It could be that a non-updated PXE server is issuing WinPE.
3. If both of those things don't work, confirm that you installed the right version of WAIK. I keep a copy with me but I 've had some customer's go out and get the Win7 version. That can work but I don' think it's supported. In any case, if you're unsure, go back through the WinPE validation process and follow the link to the Vista WAIK page.
Updating the PXE server is usually the fix though.