Michael,
The 3GHz P4 might be OK, and the 3GB of system RAM sounds great! You're using SATA drives, which is good.... but what speed (7200 RPM?, 10K RPM?), and how much cache (8 MB?, 16 MB?). Also, I'm not familiar with that video card....is it AGP, PCI-Express, or ??? Seems like the high performance video cards are PCI-Express with 256~512MB of video RAM, and costing $200~$600.
BTW, read the review of the Sony Vaio VGC-RM1 Editing Computer ($3500) here on the Videomaker website, in the Hot Gear section, just below the Forums section.
Hope I've been of some help, :)
Ken Hull