Choose Video For Windows (.avi) as the file type. Look in the template pull down menu and you'll find several DV templates. Choose whichever one is appropriate for you, NTSC/PAL, widescreen or not, etc. Click on the Custom button if you need more control over various settings.
DV Streams are the clip format used by iMovie. They have a ".dv" extension and as far as I know, iMovie is the only program that uses them.
The only way I know to do this is to use Quicktime Pro from Apple. DV Stream is one of the Quicktime Pro export options but it is not available from the codecs made available to outside programs.
Basically what you do is download the free version of Quicktime from Apple, then upgrade by paying the registration fee to the "pro" version that will let you save and export different formats. You will get a serial number that is based upon some mathematical formula applied to your name and that will unlock the extra features. You will have to do the conversions one at a time and the rendering time is pretty slow (one of the few examples where G4 and G5 chips actually are faster!).
This will also let you convert clips between Vegas avi and Apple Final Cut Pro formats, You can do this conversion with Vegas accessing the Quicktime formats, but the resolution will be scaled down unless you do the conversions with Quicktime Pro directly. If you are doing a clip or two this is fine, but if you are doing a whole bunch of clips, batch files from Vegas are don't output clips good enough to be useable. You have to do them one at a time from Quicktime Pro as well.
No need to buy QT Pro, just install the free version of QT with the authoring componentns, then render from Vegas as .mov using the QT DV codec. FCP can read these files as is, and will also treat them identically if the extension is changed to .dv
My first video project started on a Mac with iMovie, was moved to FCP, and finally ported over to Vegas.
It's been a couple of years since I did this, and it was with an earlier version of QT and Vegas, but I have found that renders from Vegas using the QT codecs were of terrible quality. I faulted Apple for this, not Vegas, since Vegas was just accessing what QT made available to it. Has this improved with later versions of QT and Vegas?
As far as using DV Stream clips with FCP, when I tried this a few years ago, it put quite a strain on my Powerbook. The software could use the .dv files, but the extra on the fly conversion was too much for the G4-500 to handle. Maybe this too has been improved in later versions. My experience was with FCP 2 and with clips captured in the DV Stream format with iMovie. I had too convert each clip with QT Pro before I could use them smoothly with FCP.