How do I compute Cohen's d in SPSS and its confidence interval in EXCEL?

Cohen's d represents the difference between a pair of group means expressed in terms of the average group standard deviation.

Cohen's d = (difference in group means)/(average group sd)

This may be worked out using the routine of Smithson which is located in the demo file in the power talk given as part of the Graduate Statistics Courses 2009. Alternatively the average group sd is equal to the square root of the Mean Square Error outputted using the ONEWAY procedure in SPSS and dividing this into the difference in the two means which can be obtained using the means procedure. For example for comparing the two age 'pr' group means we can run the below

ONEWAY
  age BY pr
  /MISSING ANALYSIS.
MEANS
  TABLES=age  BY pr
  /CELLS MEAN COUNT STDDEV  .

You can alternatively use SPSS Output Management Syntax (OMS) as shown here to compute Cohen's d which converts the tabular output in SPSS procedures into data files which may then be manipulated to give statistics of interest.

Cumming and Finch (2001) have written an EXCEL spreadsheet to compute the 95% Confidence Interval for Cohen's d available from here. The spreadsheet is also here. Choose the table related to the CI for d, select d using the paddle then simulate the lower and upper limits clicking on find LL and find UL at bottom of page under the plot to produce the 95% confidence intervals.

Alternatively a formula for the variance of Cohen's d is given here.

References

Cumming, G. & Finch, S. (2001) A primer on the understanding, use, and calculation of confidence intervals that are based on central and noncentral distributions. Educational and Psychological Measurement, 61, 633-649.