Music and Video editing needs can vary tremendously depending on what one is editing... (Feature film, Shorts, clips, etc...)
So rather than making up a configuration, I will just provide elements you can investigate:
1) Mobo + CPU: ($500)
Try to go with a dual CPU Tyan Mobo Such as the Tiger MP or MPX ($150 to $200), and 2 Athlon MP processors ($150 to $500)
2) Video: ($150)
Get a video card with Dual Head (so that you can plug in 2 monitors). You don't really need a fancy one in my opinion.
3) Primary HD: ($100)
Get at least a 60 Gb HD (at 7200 RPM) for installing all the programs.
4) Audio: ($200)
I would go with the Audigy Platinum which has the extension box at the front; that way all your audio connectors are easily accessible.
5) Video Editing Card: (Now is where it gets pricey...) ($500 to $3000)
You now have 2 choices:
a- Buy Adobe Premiere, and use the Firewire from the Audigy card to acquire video.
b- My favourite... Go look at
www.pinaclesys.com, and try to find something suitable for your editing needs (it goes from Home use to professional use...) These products include both hardware and software. Another thing to do is tro try and by the older (last year's) Pinnacle DV 500 Plus on E-bay. I saw some of them at around $500. This includes a break box with RCA and SVHS connectors.
If your friend needs to edit in PAL, make sure to check that the system is compatible.
Matrox also has a system that includes both the Video card and the Editing suite.
6) Editing HD and SCSI RAID Array: $400 to $3000
If your're dealing with movie editing, I would recommend getting a SCSI RAID controller, and a few SCSI HD (36 Gb each...), and get 2 or three.
A cheaper solution is to get a simple SCSI card, and then get a big 120 GB SCSI HD
An even cheaper solution is to forget the SCSI, and get a Secondary big IDE HD (120Gb), or a Mobo with IDE Raid (then look at ABIT and Gigabyte Offerings), and Strip 2 Secondary HDs.
7) Sound: ($150)
I would go with a Klipsh 2.1 system dor high resolution sound.
You should be able to get something decent for around $1,500 to $2,000.