Pinnacle Studio 8 is a special animal, and in your price range also, I think the best you could do is something like a Athlon64 3000+, and motherboard, and use your memory (if it will even boot with 2100 in there) and set the bios down to (gasp) 133. When you get money, get a gig of PC3500, but that is like $300 for the good stuff. I have Pinnacle Studio 8 and run it on a XP2400 cpu and 512 meg PC2700. It does fine. I even used it on an XP1800 with 512, and noticed the difference.
An alternative would be NF7-S and XP2500 CPU and memory, but you could only get 512 meg to fit the $300 budget, or (gasp) mix the 3200 you get with the 2100 and set the speed at 133. But then your XP1700 would be almost as fast.
Edit for Intel buffs: Pinncle Studio 8 takes about 4-8 hours (depending on the CPU) to encode the project in preparation for DVD burning. The extra speed that a P4 would give for this application is minutes if at all, as this is not the application they use to benchmark "encoding".