2 variable t-test for linear regression?

[kcallahan]

I'm working on an independent study biology essay, and I need to determine if there is a significant difference between the linear regressions for the three different data sets I collected. I've never take a statistics class, so I have no idea how to go about this and I don't have access to any professors who would be able to instruct me at the moment. So far, I was able to calculate the mean linear regression for each set of data, the standard deviation for each of those regressions, and I also attempted to solve for the standard error by dividing the standard deviation by the square root of the number of values in the data set (hope that's the right way to do that?). I'm a little lost as to what to do from there. All the information I can find is on how to do a t-test with the null hypothesis being that the coefficient of the linear regression is zero, but I want my null hypothesis to be that the difference between two of the coefficients is zero. I hope this makes sense and I would appreciate any help at all. Thank you!