I've installed XCode v3.1.3 and am having difficulties using the rumored GCC that is installed along with it. -- I'm certainly able to use the XCode IDE to compile my programs but would like the flexibility of also using the command line...
Where's GCC?
In /usr/bin you should find gcc-4.0 and gcc-4.2 and then there will be a symbolic link gcc which points to one of these (usually gcc-4.2).
As always, you can find out where any available command in your PATH is located using which, e.g.
$ which gcc
The most likely explanation is that when you installed the Developer tools you unchecked "UNIX Development Support", so the command line tools were never installed. Delete your /Developer/ directory and do a clean install of the tools; make sure to select "configure" during the installation process and ensure that the appropriate items are checked.