I have an Asus P2B (UDMA33) and just bought an IBM 307045 and a Promise Ultra100 PCI controller card. All I have to say is <font color=red><b>WOW!</b></font color=red> The difference is more than noticeable. Pay the $45 for the controller, IT'S WORTH IT!
I threw my old drive on the card's second controller for paging, and both my CD-ROM drives are on the two on-board controllers. I've got Win98, NT4 Server, W2K Pro, and W2K Svr and they all have been working without a hitch.