Snow Leopard restarting

Try booting into Safe mode

<http://support.apple.com/kb/ht1564>

This will not load any 3rd party additions, it will load some more conservative Apple drivers (may cause screen flicker), and it will clear some kernel caches (a cache is saved data in a form that can speed up a program, but is totally redundant to the original source, and thus can be safely cleared). Booting into Safe mode is just an experiment, but can frequently eliminate any 3rd party interference, or a cached item out-of-sync with the world. (Verify Safe mode via Applications -> Utilities -> System Information -> Software -> Boot Mode -> Safe vs Normal)

It is possible some software already had installed is not playing nice with Snow Leopard. Safe mode may allow you to get past that.

Have you tried shutting down the computer using the power button and then restarting?

Startup Issues - Resolve

Startup Issues - Resolve (2)

Startup Issues - Resolve (3)

For the System information, hold down the option/alt key and click on the  menu. Choose the first option. It may have been named System Profile in Snow Leopard.

Did you try the links I posted?

reinstall, making sure you erase the partition before install, you should be fine