I downloaded the source code to Quake 2 Evolved from http://www.quake2evolved.com and then did the following:
- created a Carbon based project
- added the Q2E source to the project
- added the OpenGL and OpenAL frameworks to the project
- hit 'build'
I then get the following error (removed non-relavent details):

qshared/q_shared.h:138: error: parse error before numeric constant

below is a snippet from the file, with line 138 corresponding to the the 'typdef enum' line:

Can anyone suggest what could be wrong?

my guess is that something has #define'd true and false to 1 and 0 respectively.

you can check that by using Xcode's "preprocess" command and searching for this line in the mess that results.

if that's the case, you can probably fix it by #undef'ing false and true before the enum declaration.