This excerpt taken from the WINN DEF 14A filed Sep 22, 2008.
Can participants sell the stock that they purchase under the ESPP?
A participant may sell all or a portion of the ESPP shares at any time. Shares may not be transferred to another broker or to the participant until they have been held in the account for at least two years (although they may be sold at any time). Shares held for at least two years from the date of purchase generally qualify for more favorable tax treatment.