The last news on the tigcc site (http://tigcc.ticalc.org/) says that the UAC can break the compilation process if the UAC is activated (MS Vista, 7).
It seems that on Win XP, if the account used to compile with GCC4TI is not an admin account, the same problem occurs : http://www.mirari.fr/FYoM
The project is Venus, by Zephyr : http://remi.caput.fr/ti68k
At home, I can compile it with an admin account on Win XP (sp3).
I'm trying to do more tests.