Vista has a preview screen in disk explorer which will show text files and word docs as well as PDF files created with adobe, but PDF files created with doPDF do not preview. Is there a switch to throw or a place to add the necessary instructions and if not will this be available feature in doPDF?
Can you open those pdf files created with dopdf? If the pdfs can be correctly opened I don't see any reason they will not show in the preview, unless the .pdf extension is not associated correctly (but then again those created by adobe shouldn't show either).
There's a thread over at adobe http://forums.adobe.com/thread/303008 that discusses a bug on Vista 64, maybe that's something applicable in your case too.