I'm no expert, but I've wanted to do the same thing. There is a lot of info around on connecting an lcd to the parallel port to get the same info as the matrix orbital units but a lot cheaper. There is also some good freeware to avoid having to learn any code if you'd rather not. Check this out.
http://www.overclockers.com.au/techstuff/a_diy_lcd/
Wolfy goes through the whole thing step by step and gives links to sources for parts & software.