declare @foo table (drive char(1),mbfree int)
INSERT INTO @foo EXEC master..xp_fixeddrives
IF @@rowcount = 26 
	SELECT '*' as drive
ELSE
	SELECT TOP 1 drive FROM @foo ORDER BY drive

declare @foo table (drive char(1),mbfree int)
INSERT INTO @foo EXEC master..xp_fixeddrives
SELECT * FROM @foo