This might not be the right area of the forum but since 'Xvesa.tcz' is not your "typical extension" I decided to post it here:
When comparing the ownership and permissions of the Xvesa executable from the Xvesa.tcz extension with the (TC) core file one sees the following:
-rwsr-xr-x 1 root staff 650048 May 20 2009 /usr/bin/Xvesa
-rwxr-xr-x 1 tc staff 1335056 Oct 25 23:20 /usr/local/bin/Xvesa
With these settings I only managed to run startx (which is meant to use /usr/local/bin/Xvesa) when run by root (e.g. 'sudo startx').