An A1C test is not a direct measure of blood glucose, although the two can be correlated. Because of differences among labs in how they calculate A1C, and differences among individuals, conversions of A1C to blood glucose aren't exact. But they can give you an idea of what your average blood sugar has been over the last few months.
The Diabetes Tool Box, a service of the Diabetic Drug Store, has an online calculator that can convert your A1C reading to an average blood sugar reading. Try it!
Update - June 2008: If the above doesn't work, try ACCU-CHEK's:
Or you can get a sense of the relationship between A1C and blood glucose from the following table, excerpted from the American Diabetes Association's (ADA) 2005 position statement on Standards of Medical Care in Diabetes:
and Mean Plasma Glucose Levels
For the ADA's 2005 Position Statement:
Standards of Medical Care in Diabetes, Diabetes Care, 2005