Can anyone tell me how I can burn a DVD on my Mac from imovie?
I have several times "part with iDVD" tried but I think iDVD not.
If you iMac came with Lion or Mt. Lion pre-installed you will not have iDVD on your Mac. That's becuase Apple has stopped support of iDVD and with the release of Lion is no longer providing iDVD (and iWeb) with new Macs.
To get iDVD you will need to purchase a copy of the iLife 11 disc from a 3rd party retailer like Amazon.com, eBay.com or whatever is available in your part of the world.