'99 Chevy Blazer - Temp. Gage & A/C

When I was driving back from lunch today, the A/C in my '99 Chevy Blazer suddenly started blowing lukewarm air and the "check gages" light came on. I checked all gages and the only one that alarmed me was the temperature gage inside the vehicle. It was at 260 degrees (the highest temp. Possible on that gage). The car was still running fine and made it back to the office. I'm afraid to drive it home for fear that it will overheat or conk out on me on the freeway. What do you think is wrong with it?