datetime to minutes?

hey all, i need to find the ratio of difference in 2 datetime variables and the difference of another 2 datetime vars. I figured the best way to do it is to convert the difference in both numerator and denominator to number of minutes.
can anyone help ??I'd use something like:SELECT 1e2 * DateDiff(minute, colA, colB) / DateDiff(minute, colC, colD)
FROM myTable-PatP