if you actually BUY logic studio it's absolutely no problem to install version 9 over your existing logic studio 8 installation. that's what the installer has been made for (get the upgrade, it's just 199 afaik). it shouldn't be a problem to install the upgrade over your current setup as long as you didn't delete major parts of the installation. hth.
I managed to delete all parts of Logic 8 and installed Logic 9 ok. The reason it still wouldn't open is because Logic 9.0 isn't compatable to OS X Lion so i downloaded the free upgrade to Logic to v9.1.5 (i think) and now it works.
Although i see that Logic 9 has changed all the good shortcuts like '*' for record and '00' to take the marker back the start of the arrangment.
Thanks for you help