I did a quick look at according to dpreview.com, the files it creates are Motion JPEG .avi files.
Do a search on motion JPEG on this forum and you'll read all about it... bottom line is that depending on your version of Vegas software, you may need to get a motion JPEG codec installed on your system.
Sony had a bug on their mjpeg decoder and the D90 footage wouldn't work. However, they did fix it a few months back, and the fix did show up in Vegas Pro. It's just that they didn't push the fix on Platinum too. So what you need to do is email them and ask them to push the fix on Platinum too.