I have a Powerbook G3 Lombard (bronze) which I would like to instal osX on. Others have said this is theoretically possible, but could one change out the processor and make the computer much faster? Also can a video card be accessed?
Currently, I can only use dial up and to buy a new computer is not cost effective considering that the speed of dial up is the limiting factor. So fixing up the old Lombard may make sense.
Could anyone name a tech. company who could do this?

Even upgrades that are technically possible for laptops generally aren't worth it, with the exception of memory. I'd recommend adding more RAM, and the install process is simple enough that you can probably do it yourself. Anything else in the computer probably isn't worthwhile upgrading, your money would be better spent buying a new machine.

With regards to running OS X, Panther (OS X 10.3) should run fine on your laptop if you're not doing anything too processor-intensive. A new copy of Panther off eBay should run you up about $20.