After the Update from 10.5 to 10.6 i had the same Problem: Horizontal Rainbow Gradient/distorted Picture.
My Solution: I test with an borrowed (same) Adapter from my friend and i had a perfekt Picture. The difference between the Adapters: His Adapter is marked with the Word "PAL" (between the Connectors). It seems: Apple sells different Connectors in Germany!
So, now i try to get an replacement from Apple or ASP.
Totally stoked to confirm that 10.6.3 solves this issue for me too. Plug my Early 2008 Macbook Pro 17" into TV, then unplug, sleep it, wake it up, and then plug it in again - still color. No more black and white. Cheers, Apple.