Note that I did the below with SigmaPlot 4.01; a few things may be different
with later versions...

1. Put in data into sigmaplot (first column for X - the substrate
   concentration; second column for Y - the rate; you can label the columns
   by right-clicking with the mouse above them and hitting "column titles").
2. The best way to create a graph is to highlight the columns, right-click in
   the "Notebook1" thing on one of the "Data" sections (or click on "New" for
   later versions of SigmaPlot), choose "Graph Page", then click "Yes" when
   it asks you if you want to create a graph. This puts the graph on a new
   graph page instead of on top of any other graphs.
3. Do "Scatter", Next, "Simple Scatter", Next, "XY Pair", Next,
   make sure the columns are right for X and Y, hit "Finish".
4. Right-click on one of the points on the graph, select "Fit Curve",
   select "User-Defined", then "New" (unless someone has already put it in,
   then hit "Edit Code").
   For the Equation:
     f = Vmax * S / (Km + S)
     fit f to v
   For the Variables:
     S = col(1)
     v = col(2)
   For the Initial Parameters:
     Vmax = [whatever you got from a Woolf or Lineweaver-Burke plot]
     Km = [whatever you got from a Woolf or Lineweaver-Burke plot]
   For the Constraints:
     Vmax > 0
     Km > 0
   The Options should not really need changing.
   Then hit "Add As" and give it an appropriate name.
5. Hit "Next", make sure the columns are right, hit "Next", you should get a
   preliminary R-squared and the values of the Vmax and Km calculated, with
   a "Converged, Tolerance Satisfied" or similar message (if not, ask
   Dr. Kahn or myself). Hit "Next", the only thing checked off should be
   "Report", then "Next", you want to "Add Graph to Curve 1" (or whatever
   your curve is numbered/named), hit "Next", the "x column" and "y column"
   should both be "First Empty", hit "Finish". You should now have a line
   for the curve on the graph - make sure it looks reasonable! - and a
   "Report" which you should hand in along with the graph, except trim off
   the "Influence Diagnostics" line and everything below it (leaving the
   "Regression Diagnostics table and everything above it). The Report gives
   you the R-squared ("Adjusted Rsqr") and coefficients of the equation.