bought a vulcan for the wife on ebay. it's located in Maryland and I need to bring it home to NY.

Can I just throw my plates(from my bike at home) on her, buy insurance and ride her home?

Just get a written bill of sale and insurance (with a printed email or something as proof) on the bike. Don't put tags on it from another bike. That's asking for trouble if you get pulled over. I rode my bike around for 3 weeks in and out of 3 states with no problems. Cops are pretty cool to bikers as long as we're not acting like squids and respect traffic and the laws.