As far as I understand you need to get your hands on an install DVD for the MBP and update the drivers from there. If you can't get your hands on one you could of course try downloading a disc image via a filesharing site, but you do this at your own risk. OS 10.6, also known as Snow Leopard, is actually only about $30 to buy and is a big improvement on 10.5. You could always go to an Apple Store or buy it online. I think using Disc Utility, which is on the install disc, would verify your disc permissions and identify the missing drivers. Alternatively you could do a fresh installation.
Hope this helps.