Dont discount older stuff?
No, thats so true
Among my own best PCs are a P4 3.6 with 2GB RAM, and I have tried and tried to get it to play games like the AMDs and I am still not at all impressed... Even this so called encoding is a fair bit slower, or at least converting AVI and VCD to DVD using TMPGEnc is poor on the intel and the AMDs are pretty much 5 times faster ( 10-12 minutes on AMD, just under an hour with the P4 )
The best speed I have had with older AMDs are 3.0Ghz on an XP1700, 2.9 on an XPM2500, and 3.0 on a Winchester... All of which absolutely kill the P4
Will the RAM from your Intel go into the AMD?
Will the GFX Card?
To be totally honest mate, I have avoided using Intel for some years, I only got the P4 cos it was a steal ( Not literally ) and I certainly have no intention of EVER getting another one... Its a pile of junk. I have a Smepron3100 thats better at pretty much everything than this Pentium.
I would swap them over now, accept that for a while you will lsoe a little bit of speed, but then concentrate on getting that AMD sorted... The end will be a grin so wide, your head will fall off!!!