I did it
After spending hours reading various forums and posts (none of which directly applied to my case, either because of different hardware, or newer software, etc.), I installed the 128GB Crucial M4 SSD as my main boot drive and the 1TB WD drive in the Optibay expansion (in place of the Superdrive).
The machine is actually slower in some respects, though this might be a result of poor tuning. It is lightening fast at waking from sleep, and at first was really quick in iPhoto, but after I made a mistake in migrating part of my HOME folder, ending up breaking it and requiring a re-install, the performance has been mediocre/not better than HDD. Will not bother with the hassle of re-installing again, but surely if done right and tuned correctly, performance gains are possible. THe downside is that startup time is much longer. Seems that the system is a little confused over the Crucial M4 drive at first during the boot cycle (just a guess), as this was not an issue when I had 2 HDDs running on the machine.
Anyhow, if you have a healthy old-timer 2007 MBP model number A1226, then installing an SSD might be worthwhile.
EDIT! See comment below by mbh. After selecting SSD as "startup disk" in System Preferences, the start-up time was much shorter.
