2nd Internal Drive with Leopard?

Ok, I have Leopard installed on my Mac Pro.
Quick and simple to do, and seems to operate just fine!

However, my main application, Hauptwerk won't
release a "Leopard" compatible version until later in
November.

But, I still have the previous OS, Tiger, installed and
operating just fine on a separate HD, along with
Hauptwerk. Only constraint is that no more than 4GB
of data can be used in HW, Tiger is 32-bit. Thus the
desire (need) for going to Leopard and the full 64-bit
RAM use. Several of the larger pipe organ pipe sample
sets use much RAM, up to 8 and even 10 GB (thus why
I had been using XP-64 in my previous AMD powered PC).
The author of Hauptwerk is now "urging" the use of the
Mac because of the wonderful MIDI handling of that system.
And the Pro is SO quiet it is wonderful, while my PC
put out a LOT of fan noise, etc. Not good during quiet
music passages!

I have Leopard installed to a separate HD in the Pro. But,
when HW is made available for OS X 10.5, there will be
no special reason to maintain Tiger on the separate HD,
and Leopard could also be installed on that drive.

But should I? Or what else can I do with a second internal
HD? (I do have an external HD which is the "Time Machine's"
houly/daily/etc. backup, so that takes care of the need for
file, system back ups). Cannot go to some kind of RAID set
up, UNLESS I erase both internal HDs completely; don't really
want to loose all that programing I have done for particular
organ sound systems -- took hours!

Thanks for comments, Jim