Just had to check this thread again as I've now got some spare time to get this sorted.
I'm also on 10.5.8 and bought the 10.6.3 CD on the advice of everyones posts here, can you all confirm that to do this you bought the 10.6.3 CD? I have the CD too but when I put it in nothing happens.
A) I have a broken CD
B) I'm trying to install the wrong version?
Your help is appreciated