Making Mac OS X Work Like X Windows?
X Fiend asks: "Is it possible to configure Mac OS X's window manager to run in a client-server mode like X Windows? I'd like to use my (rather anemic) iBook as an X Terminal, with apps running on my (manly dual-processor) desktop machine, but I don't want to have to use X Windows to do it- I want to use Mac OS X's native window manager. Any ideas?"
The closest thing I've seen to that is OroboroX which makes things look nativish. Or you can use Tenon X tools Click Here which apparently is built using Carbon/Quartz
If you are fine with command line there is the su command if you do a su - username
type the other user password then you are now login with that user accont.
And you can run apps as that user.
If something is so important that you feel the need to post it on the internet... It probably isn't that important.