Thanks for your info fyffe555! Its funny you mentioned about supporting it along the shaft and using open end bearings. I found a shaft (only 16mm though) that is 41" long but it has 9 tapped holes it in on one side and includes 2 open end bearings. So the shaft could be mounted down all along and include supports on each end. This would work just like a rail also. They were $89 each which I don't think is bad including 2 bearings per shaft.
They are all the way at the end of this web page.
http://store.yahoo.com/cnclinx/linearslide.html