Dummy variables and general linear models

Hi all,

I am trying to create a general linear model in SPSS with the breakdown:

How does compound x relate to cognition?

- dependent variable - compound x

- fixed factors - treatment group (0=control, 1=low treatment, 2=high treatment) and gender

- covariates - cognition, BMI, age, blood pressure.

I was told to use dummy variables for the treatment group which I've created. Reference group is control/0.

My question is, how do I run the GLM with the dummy variables? do I put the low treatment(1=low treatment, 0=not low treatment) and high treatment(1= high treatment, 0=not high treatment) dummy variables in the fixed factor and then remove the original treatment group variable? Do I need to look at anything specific to treatment groups once GLM is run?

thanks in advance for any wisdom.