I would first ask what primary aspect ratio you will want to utilize? If it is a slide presentation then do you want the 4×3 when showing HD footage to be letterboxed or do you want to expand it so you fill the 4×3 with the HD footage.
Why don’t you try both with a start point and take a look at it? Create a timeline for the HD first, and then do the same for DVCam 4×3 format, and take a look to see what they each look like.
In my experience, when it will ONLY get projected onto a big screen at a meeting, then letterbox the HD and go with 4×3. Resolution might be a non-issue depending on the projectors. Better to find out what kind of projectors and start from there.
Greg Ondera