I received a used 1.25GHz 17" (1GB RAM, orig 80GB HD) for Christmas this year - it's in great cosmetic shape and I always wanted one - the wife found it locally on Craigslist.
I ordered all the upgrade parts and did the upgrades yesterday.
What I ordered:
1GB SO-DIMM (the "user-replaceable" stick)
1GB DIMM (the "non-user-replaceable stick)
PRAM Battery
120GB SSD
SATA to IDE adapter
(already had Arctic Silver heat paste, correct Torx drivers, SATA USB dock, and some velcro tape)
Tips:
1. Use the ifixit guide - it has pics of this specific model, the xceler8yourmac guide is the 800MHz model (heat pipes and location of drive bay screws are different)
2. I had everything installed (OS X 10.5.8 and apps) the way I wanted it and made sure it ran with the stock configuration. I then installed Carbon Copy Cloner and cloned the internal HD to the SSD using a SATA USB dock.
3. While you have the unit totally open and drive bay removed, vacuum/blow out the years of accumulated dust. Use a pencil to hold the fan stationary so the air blower doesn't over-spin it.
4. Replace the PRAM battery while you have it open.
5. The SSD is way smaller (physically) than the original HD. I used velcro to mount it to the DVD drive enclosure and ensure the SATA/IDE adapter pins lined up the same as the original drives connector's did.
6. Use a single sided razor blade to remove the old heat transfer compound and isopropyl alcohol to clean the heat pipe surfaces once you've "shaved" the old stuff off.
7. Make sure not to apply too much new heat paste.
8. Take your time buttoning it back up - ensure no pinched cables and that all the screw holes line up.
Crossed my fingers - hooked up everything and hit the power. Booted up first try and running pretty snappy (for a decade old machine).
Good luck.