using wood for a computer case

I want to build my own computer case.  Is plywood a viable medium, assuming I drill holes/etc. for proper ventilation, and do something about potential dust problems?

i want to build my own case because i want to put two power supplies in the case and run my video card off of a separate psu.

Yes, and it's been done before:

http://www.silentpcreview.com/article237-page1.html

Though personally, I'd recommend a metal mesh layer on the inside of the case for ground and EM shielding purposes.