I think you'll be hard pressed to building both machines within that budget. For the PC aiming to spend around £500 / $850. This will insure you buy a good motherboard and some stong components which u will be able to upgrade as you go. As Mike suggested I'd have to agree the Asus A8n SLI - Delux/Premium are fantastic platforms. I'm running the delux on my main system and it handles all i throw at it. It has great sata raid facilities too - 8 sata ports!!!
As for the duplication machine I found this in google - I'm sure you may be able to find something cheaper over there in the states but this is a good benchmark for prices but at roughly $700 its quite high.
http://www.magellanhardware.co.uk/ma...ucts&serid=123
Video cards - unless you doing high end 3d a standard 256 dual head card will do. It doesn't need all the bells and whistles but something with stong Open GL engineering is always a help especially if doing lots of compositing or after FX work
Mike suggested a 430w psu - The bigger the better - If u are gonna have multipe hard disks a 550W is a min requirement. Sata drives suck up the juice.
Seymore - before u go there - Yes I
am biased - he he - its a proven platform and O love it - Mike is a wise wise wise man!!!