monte carlo simulation problem/application

i will explain my problem... I have made a code for finding fourier transform for discrete sample..and plotted the final result..now I have a plot of fourier coefficient vs time lag..I have to test the strength of the peak fourier amplitude by using monte carlo...steps to be followed are as follows

step 1: i have to fit the data plot(nnot the final plot which i got after running fourier code) with some low order polynomial (this i can do by polyfit command of matlab...right??)suppose i get a 7th order polynomial as best fit..

step2: now i have to find de trended plot...i.e i have to subtract the polynomial curve from the original curve..how will i do it?

step 3: then i have to obtain probability distributions of flucuations. (which again i want to know how to do)

step 4: using this probability distribution i have to do random sampling of a random plot with statistical properties same as the original plot.

Step5: then taking EACH combination of these generated plots we have to run the code for fourier transform(which i already have) on each pair possible and thus find fourier coefficient for each pair.

pleaasseee help me out...