The link below will take you to pics of the flexy stand I built for my 32" TV and the flexy stand that now goes around my 47" RPTV that replaced it. I hadn't finished the riser for the RPTV when I took the pics hence the ackward space between the top of the TV and the shelf above it.
http://photos.yahoo.com/ryan_schnacke/
My stand for the 32" TV is about 42" wide x 20" deep x 25" high. 5/8" all-thread rods. Holes are 1" from the edge of the wood (the edge of the holes, not the center of the holes). This allows 19" between rods which is just enough to slip in a standard width component from the front or the back.
The following web page is VERY useful for determining whether or not you have enough support for your shelf spans when using MDF. I used 3/4" birch veneered ply and I would imagine that it is at least as strong, probably stronger than 3/4" MDF.
http://www.pbmdf.com/buyerguide/TBShelving3.htm
When you drill the holes you may want them just a little bigger than the rods. It can sometimes take a bit of effort to slide the wood over multiple rods at once. This is especially true when you've got six or eight rods. I drilled them with a 5/8 bit and then used a Dremel tool with a sanding bit to widen them just a little. Worked great.
If you attach castors to the bottom try to keep them as close to the all-thread rods as possible. The weight gets transferred from the rods to the wheels and you don't want it to have to be transferred a large distance horizontally to get to the wheels or the wood will start to bend.
