How can I do standard curve calculations with replicate "unknown" measurements?

With nonlinear regression, this is built-in to Prism. If you enter the unknowns as replicate values, Prism will report the interpolated values on two pages (views) -- one for each replicate and one for the average. Prism's linear regression calculation does standard curve interpolations, but not with replicate values. To work around this limitation, choose "nonlinear regression" and pick a linear equation (first-order polynomial, which is the same as a straight line).