Where to direct this hardware question [upgrade amd]

[Harry Putnam]

I'm having a heck of a time plowing around online trying to find out
how much of an upgrade I can get on my thunderbird and have it be a
straight drop in.

Its a 1.2GH thunderbird on an asus-A7V-E (apollo KT133 chipset) mobo.
Can anyone coach me on this or suggest a source of answers?

I'd like to get up to 2.8GH without changing lots of other stuff.
Or would it be more practicle to get a mobo bundle already set up?