Have new 1.5 Tb drive and having trouble configuring.

This is a strange question but heres whats happening. I installed snow leopard on this new drive I bought because I use my computer for work and I did not want to upgrade my main disk before knowing all my apps work. Trouble is now every time I open photo shop it says its not licensed anymore on this machine? So the questions are a. do i have to reinstall all the programs on this HD to make them run.
The other question is since my original disc was only 250gb and now its pretty much completely full with just applications and running pretty slow, how do I go about sharing apps between the two drives if I do decide to make both disks leopard snow? Can I just drag the application folder over to the new 1.5 tb disk.
Basically I want both drives to act as one large drive with multiple partitions.
Sorry if my question is vague/


This is what I am doing
I boot from the snow leopard drive,
I open photoshop cs4 from the applications folder on the HD with 10.5.8 on it
There is an error saying that photoshop needs to be re-authorized.
Do I need to reinstall photoshop on the leopard snow HD if the HD that photoshop is installed on is running 10.5.8?
In the future say I install snow on both drives. What if I install a program like photoshop or logic studio on only 1 of the drives. Does this mean that all the third party plug ins that I have must be installed on the same disk so that there accessed correctly?