To get the best performance out of it I would recommend upgrading the OS, but 10.4 will work fine with an SSD. I recently helped my friend with his system upgrade and we put (4) 32GB SSDs (NewEgg had a great deal going) into his MacPro Intel. We used the software RAID built into the OS to do a stripe for speed. All his data is on a Drobo attached via firewire so only apps are on the SSDs.
First off a note, you won't see any performance increase to be blunt with just one SSD, the write speed pretty much kills the read speed gains for most drives, however in a raid format... OMG. Yeah, the speed increase was exceptionally noticeable. I'm sure a small part was upgrading to 10.6.x cleanly and reinstalling his apps so it's a flawless system but even I made a comment it felt like he bought a brand new tower and his MacPro is a first gen intel.
The only hiccup we had through the whole process was on first boot after the OS install, it hung for about 2 minutes then suddenly launched. We don't know why... blank screen, nothing on the display just blackness. We were about to hit the power button when all of a sudden the chime came, the gray apple, and the OS booted in like 12 seconds.
We have also noticed that the fans run a lot less, I'm assuming because he removed the 3 beastly hard drives he had in there, since the SSDs pretty much run cool the only time the fans seem to kick in would be during number crunching now.
He does graphic design and some light video work (for migration into flash), so far he's been thrilled with the speed of the apps. His data is still on the Drobo so loading docs didn't really increase in speed, but the applications themselves did. An example, Safari, you click the button and it's on the screen instantly. It's kind of crazy.
For anyone considering it, I would suggest a raid setup to get the speed... also remember you're not going to get the storage space unless you want to dump a few grand, so if you have an intel with 4 bays, maybe 3 to SSD and one to a large HDD? You will still see a nice speed bump for sure. We're happy, heck I'm even thinking about doing it at my work now!