To run a GLM Univariate analysis, from the menus choose:

Analyze
General Linear Model
Univariate...

Click Reset to restore the default settings.

Select Income after the program as the dependent variable.

Select Program status as the fixed factor.

Select Income before the program as the covariate.

Click Model.

Select Custom as the model type.

Select prog(F) and incbef(C) in the Factors and Covariates list.

Select Main effects from the Build Term(s) drop-down list and select the main effects to the model.

Select prog(F) and incbef(C) in the Factors and Covariates list.

Select Interaction from the Build Term(s) drop-down list and select the interaction term to the model.

Click Continue.

Click Options in the GLM Univariate dialog box.

Select Estimates of effect size in the Display group.

Click Continue.

Click OK in the GLM Univariate dialog box.

These selections produce a model with an interaction between the factor prog(F) and the covariate incbef(C).