What I think is you should (seriously) throw that machine away and spend $500 on a PC or laptop from Costco.
Upgrading an old AMD 1.4ghz CPU????? And you clearly know very very little about this topic so fixing up the machine will be a pain.
I mean no offense by that, there are like a million things I know jack about. But this is one that I do and I wouldn't recommend any friend or relative fix up and old machine like this themselves.
You've got a built 4Runner rig so I assume not broke. Wait for Black Friday and buy a machine from Costco. You won't be disappointed!
If you insist on fixing that machine:
* Install Win x64 not 32. This costs $$$.
* Find a comparable higher amd cpu and swap it. This is probably cheap but requires tech research.
* Throw away the hard drive and buy an SSD then install Win x64 on it.
Edit: don't mean for this to sound mean, I just don't wish for anyone to waste a bunch of time.