Sure you can! All these people who say you can't without destroying the 'HD' quality have NO idea what they're talking about. Here's the deal:

The VAST majority of Blu-Ray discs are encoded in the old, crappy MPEG-2 format. The same MPEG-2 format as DVDs. Yep. Blu-Ray is still encoded at the same bit-rate and by the same codecs as DVDs, with very rare exception.
Now, the difference is that Blu-Ray uses a 'more precise' (not the best term to describe it, but it's kinda like precise) beam to burn data closer together, thus leaving more room for other stuff. But as far as destroying the data? Wrong.

Now, for the problems:

1) You are SEVERELY limited by the smaller size of the DVD (even DVD-DLs are less than half the size), meaning that you can't fit the average length movie on one. Gotta chop it.

2) You also must have software that will allow your current DVD burner to do it correctly. This can be kinda hard to find.

3) You have to know how/what format/bit-rate etc. to encode your projects so it will look good. This requires you to know how to edit with more than Windows Movie Maker.

I own a videography/editing company, and the editing software I usually use, Sony Vegas 8 Pro, will allow you to do it, although it's not a well-known or 100% fool-proof method.