I would save your pennies until you can buy a new Mac rather than trying to upgrade the processor, etc. I've done both over the last 27 years (eek!) and in the end it was better not to go with third party upgrades for processors. RAM and HD, yes -- processor, no. Overclocking is also not a good idea.
Save your pennies and get the real thing in time.
Also, evaluate why you feel the need for a new machine. We too have older G3's and one G4 in our household. The G3's are good enough for OSX 10.3.5 (and probably 10.3.7) as well as all the software we use (word processing, spreadsheet, database, email, web, Photoshop, Illustrator, GraphicsConverter, most games, etc). The one reason I, and my sons, would like to get a screaming fast new machine is X-Plane flight simulator which could really use a lot more VRAM and processing power than we have on even the fastests (500MHz G4) of our machines. So, we're saving our pennies. 🙂 It is hard to justify the thousands of dollars for the machine we want just for a mere game... 🙂 But we're trying!
Cheers,
-Walter
in Vermont
-8F this morning,
the ice is smooth,
the snow is squeeky,
the sheep say bhaah
and the pigs say oink.