Beepster
The consensus seems to be that there is something going on with your access

This is a known problem with the C++ libraries and a Win 7 install from the DVD.  It must be installed by a logged on administrative account (not run as admin) to get past the reboot.
 
Glen

Success!  It appears that the rebooting problem was related to the bug in the X3 installer on DVD versions that Glen called to our attention.  I contacted Cakewalk tech support and the person I spoke with wasn't familiar with the "bug" but sent me a link to the download version of X3.  It installed properly the first time I tried it.  I tried installing the DVD version on my wife's computer and it worked fine there, so it appears to only be a problem with computers with certain types of other software installed, as Glen mentioned.  Cakewalk really should have an update file that fixes this problem for those using the DVD version.  Thanks for all the helpful comments.

> so it appears to only be a problem with computers with certain types of other software installed, as Glen mentioned
 
Or (more likely I suggest) group policy restricting access to certain software being installed from removable devices :)
I doubt this is a cakewalk issue, more a conflict with other software or permissions (otherwise it wouldn't cause a reboot, it would just stop with an error). Glad you got it resolved..

Well it was repeatedly stated by the Bakers that there was a problem with the DVD release... thus the extremely prompt "a" patch. The initial download release resolved this issue (without the ensuing patches) so this makes sense... I guess. I wonder if the boxed sets currently being shipped have been updated.

Hmm maybe they tried to write to the DVD whilst installing....!

Sorry. I didn't read the second page of posts and didn't see it had been solved. All the best.