Wife and I are doin Thai, Laos, Cambodia and Vietnam in Dec. ANYWAYS! We are getting our Viet. visa at the embassy in Korea. Can we enter Vietnam at the border crossing or does it have to be by air only?

The visa application form asks you how and where you will enter the country.

If you state overland and name the border and they grant the visa then you should be OK.

Otherwise they'll tell you that you cannot enter at that border, so pick another border.

The staff at the VN Embassy is Seoul are very good and helpful.