20 GB? Whoa! I don't think so. They are deadly expensive. I got a SimpleTech 1.8 GB which is a rebranded Bitmicro for $1,139.61 U.S.
http://www.cdw.com/shop/products/default.asp?EDC=450930

I partitioned it 1GB FAT32 for the boot up and ROM and 720MB for Persistant Home. Storage is a share on a Win2K server.

Oh, I should mention that I built three boxes and sold two to off-set the cost.