Dashken will show you just how simple that is with a nifty little tool call IfoEdit. Here's a quote from the guide :
Now, why would any person want a continuously looping DVD movie or video clip? If you are a hardware tester, doing so allows you to test the stability of the PC, the DVD decoding software and the DVD drive. It's also useful for those who want to do presentations at an event (like a technology fair) or even loop advertisements (at banks and electrical stores). In such cases and many others, an endlessly looping DVD may be just the thing you need.
Check it out at TechARP.