Celeron upgrade questions

[P T]

I built my own system a year ago (athlon 1700+, k7s5a, etc.) so I'm
fairly familiar with stuff.

My brother has an old eMachine with ~500MHz Celeron, 2 x 64 mg sdram
pc100, a 40g hd, Windows98. I suggested he could get a Celeron about 3x
as fast for ~$50.

Questions:
Is there a limit to the speed of the Celeron he can put in?
Would a new Celeron work seamlessly with his hard- and software, or
would it have issues?
Are all Celerons the same socket config?
Would the old heat sink work?
Would his cpu fan (if he has one) work on the new heat sink?
Would he notice any improvement (mostly just surfing w/ dial-up)?
Anything I'm missing?

Thanks
Pete

 

[P T]

Okay, after I posted, I did what I should have done first... went to
google and searched usenet... I think I know what the answer is now...
there's only one way to upgrade that system...