Under NCAA football rules, is it possible for a team to score a single point in a game?

No, the only single point scoring plays take place after a touchdown. Therefore, the team attempting the extra point would have already received six points for the touchdown.

There are, however, very rare single point safeties that can take place on extra point attempts, also known as a try. If the defensive team blocks the attempted kick, it's possible to recover the kick and then get tackled or fumble it out of bounds in their end zone, the resulting call is a "try safety".

Here's a video example of such a play:
http://www.youtube.com/watch?v=jp4TeP4rw0s

When a college game is forfeited, the score is set at 1-0.

In 1910, Baylor disputed a referee's call and walked off the field. Texas won the game by forfeit with a final recorded score of 1-0.

JACK MAGUIRE'S "TALK OF TEXAS"
November 20th 1998 | by Jack Maguire

It began on November 5, 1910, when the Univer-sity of Texas and Baylor played in Waco. Baylor archives say the game was a 6-6 tie, assuring the Bears of an undefeated season. UT records claim the Longhorns won on a 1-0 forfeit. Texas scored first when a Baylor fumble was blocked by its own team. The Baptists debated the call and delayed the game. Then Texas fumbled and Baylor scored and Texas claimed the Bear had stepped out of bounds. Later a Longhorn back dropped the ball while trying to pass and Baylor picked it up and scored. The referee ruled that the ball had touched him and thus the play was dead. The angry Baylor team walked off the field. Since each team had scored once, the Bears claimed that it was a tie. Texas claimed a forfeit. After 88 years, the argument continues.

A similar conflict erupted on November 21, 1919, between Rice and Howard Payne in Houston. Rice scored early. In the fourth quarter, a Howard Payne pass bounced from the hands of its receiver to another and he scored. However, the referee ruled that it had been touched by a Rice player and was an incomplete forward pass. The angry Howard Payne coach took his team off the field. Rice was declared the winner by a one point forfeit.

http://www.southernlivestock.com/articles/columnists/jack_maguires_talk_of_texas.4194.sls