I have just had a new room built which I will be using for editing & recording (ADR & Vocals etc). The room is very quite at the moment, but I know that as soon as I put the computer in there, noise will follow!!

I don't have the luxury of housing the computer in a separate room, so I was toying with the idea of putting it in an acoustic enclosure.

So, does anyone have any tips for building an acoustic cupboard that will both drastically cut down on noise and maintain a good airflow ?

You should go with a quiet pc set up.I ordered a new audio rig from PCaudiou in California for a client of mine. I specified their most quiet enclosure, and it's so quiet, you can't even tell that it's on. So after hearing( or NOT hearing) that, I bought the components to do that to my own music rig.
Here's what I bought ( haven't had time to put it together yet).
1-Antec "sonata II" quiet case.
2-Zalman "Ultra quietcpu cooler (fan)"
3- Acoustic foam specially formed for this case from Quiet PC USA ( but I think the stuff comes from the UK-www.acousticproducts.com.
This way I'll be able to keep my computer in the same room I'm recording in , minus the noise.
Good luck
Bruce Yarock

CNET.com has a pretty good DIY recipe for soundproofing your computer.

http://reviews.cnet.com/4520-11319_7-5670307-1.html?tag=txt

I've never tried it myself, but it sounds good to me. I have a Powerbook G4, and it's very quiet - never interferes with any recording.

Steve

There are also cooled enclosures for your CPU/tower made specifically to silence the system completely. Using the Matrox 650, and liquid cooled system, there is zero noise from my main box. The hard drives are rubber-mounted, so it's the only real moving part in the box. My drives are predominantly elsewhere, just the boot and secondary drive in tower. The DVD Burner is noisy when burning, but I don't use that during recording anyway.
HTH