The ._ files you are seeing on the flash drive are resource fork files the Mac is saving to it, similar to the random thumbs.db and other files Windows systems save to disk. You can delete them without any harm, though the Mac will keep putting them back. Basically it's really bad legacy stuff that I hope Apple just fully kills off soon.

As for printer sharing, it's easy. As Dignan suggested, download Bonjour for Windows to add the protocol Apple uses for auto network discovery of resources. On the Mac, here is what you need to do to share the printer:

1. Click the Apple menu in the top left corner and pick System Preferences
2. Click Print & Fax
3. Click the Printer you want to share on the left
4. Click "Share this Printer"

You may be alerted that the system printer sharing is off. If it is, it will notify you, and present a Sharing button to click. Click it, then turn on Printer Sharing.

Once you have done the above, go to the Vista machine with Bonjour installed, and look for the Printer setup utility under the Start menu that it installed.