I read up on the new Cannon 5D a little. Do you think I will outgrow this camera too in 6 months? Or, do you think it is a good camera that will allow me to NOT invest anymore money for a while and grow with my photographic desires? Also, how much will it cost to get the lenses I can work with until I save up more money for a better range?
I'm sure Canon 5D will be a very nice camera. You wouldn't outgrow it in six months, but you likely would not outgrow a Rebel XT in six months either. On the other hand, I'll warrant that you'll be wanting more lenses and other equipment within six months to add to the capability of whatever camera you buy!
So ... some general recommendations -- take with a pinch of salt, your milage may vary, adjust to taste, etc:
a) determine how much money you have to spend
Without doing this, it's hard to limit the possibilities. If money were no object you could buy one of each model and keep the ones you preferred, and you wouldn't need to ask for advice! :-)
b) rather than starting with "which model do I want", start with "which camera system do I want".
With a SLR you're buying into a system of cameras, lenses, flash equipment and accessories. Some people prefer Nikon, some people prefer Canon. Both work and neither are bad choices. (Some people prefer other manufacturers, but in DSLRs Nikon and Canon are the big two currently.)
c) think about what focal length lenses you want
Unfortunately this becomes complex due to the "crop factor" on models like the Canon 20D and the Nikon D70s. A wide angle lens (Canon 10-22mm, Nikon 12-24mm) for these models will not work on a full frame camera body.
Note that a 20D plus a 10-22mm lens is still a lot cheaper than a 5D -- buying an EF-S lens can be sensible even if one day you aspire to a full frame camera. Nikon don't presently have a full frame DSLR: their top of the line model uses the same 1.5x crop factor that is consistent across their range.
d) look at Bob Atkins' comparison of the 20D and 5D, which I think has a good summary of the strengths and weakness of each choice http://bobatkins.com/photography/digital/c..._5d_or_20d.html
e) spend some time on the web sites of the online retailers such as Adorama
to see what cameras and lenses sell for. Relate this to your budget, increase the budget, iterate. :-)
Have fun, and remember equipment is only what we use to take photographs, not an end in itself. (OK, there are collectors of cameras who are not photographers, but they're rare around these forums. :-)