Obnoxious and unhelpful. How long have you been using Macs? I seem to remember a day when you upgraded your operating system, and everything not only worked, it worked better. Ignoring Mac OS 8.0, anyway.
And actually, on this Beige, which started out with 8.5 and has gone progressively from 8.5 to 8.6 to 9.0 to 9.2 to 9.2.2 to 10.3, 10.3.9, 10.4 to 10.4.9, it's been my experience that everything just works the way it should. Or shouldn't, in the case of Panther and Tiger on an unsupported Mac.
People were installing Mac OS X on PCs long before UB.. it's possible. I also will bet that at least 10.4.10 and 10.4.11 wil work on the MacBook Pro. If your install CD isn't UB, you can always... acquire it in other ways. After all, you did pay for both the Tiger CD and the new mac with Leopard. . .