The Sleeping Dragon

Description for THE SLEEPING DRAGON by Joel Rosenberg:

CAPTIVES OF SORCERY...
It began as just another evening of fantasy gaming with James, Karl, Andrea, and the rest ready to assume their various roles as wizard, cleric, warrior, or thief. But sorcerous gamemaster Professor Deighton had something else planned for this unsuspecting group of college students. And the "game" soon became a matter of life and death as the seven adventurers found themselves transported to an alternate world and into the bodies of the actual characters they had been pretending to be.

Cast into a land where magic worked all too well, dragons were a fire-breathing menace, and only those quick enough with a sword or their wits survived, the young gamers faced a terrible task. For the only way they would ever see Earth again was if they could find the legendary Gate Between Worlds--a place guarded by the most terrifying and deadly enemy of all....

This is #1 in Guardians Of The Flame Series.