If your HDV (.m2t) clips won't smart-render in Sony Vegas Movie Studio 9 Platinum, try running the .m2t files through VideoRedo Plus. Remuxing them seems to be the trick. Since there is no transcoding, there isn't any degradation.
1. Open the .m2t file in VideoReDo Plus
2. After the file loads, click the "Save As" button.
3. Click YES to the "Do you wish to re-mux the entire input file?" message.
4. Make sure the file type is set to "MPEG Program Stream (*.MPG)" and then click SAVE.
If you don't have VideoReDo Plus, then try remuxing with some other application. I happened to have Adobe Premiere Elements 2.0 and the Mainconcept MPEG Elements 1.0 plugin which smart renders HDV files. After remuxing with that, the file could be smart-rendered in SVMS 9 Platinum.
I didn't have any success using MPEG Streamclip for remuxing. The files wouldn't smart-render in SVMS 9 Platinum.