How do I use perform a least-squares spectral analysis in matlab

Hello,

I am interested in performing a least-squares spectral analysis on a bunch of time series to see what periods have the most intensity. I am looking to compare my results against a calculation done in excel using a macro. see Forecasting Time Series within Excel (<http://web.calstatela.edu/faculty/hwarren/a503/forecast> time series within Excel.htm)

I want to plot my results not in normalized frequency, but as a function of period. This seems trivial but it is eluding me at the present.