R help - Jan 2013 - Repeated Measures and Dependen pre-test variable

Hi,
I have an experiment where I measured two times the dependent variable (called
<b>Intention</b>). So, I have IntentionPre and IntentionPost.
I am working with an anova for an independent variable called
<b>NumberOfModules</b>.
The problem is that if I run the aov(intentionpre~NumberOfModules) I have that
there is a significant difference between the means.
I want to know the difference between pre and post intentions based on the
NumberOfModules. So, I've been told that I should make an ancova and the
IntentionPre variable will work as a covariable, but I don't really know how
should organize my data in order to get that.
My dataframe currently has the following columns: <b>Email (userId),
Intention (pre+post values), constrast (is it pre or post value?), and
NumberOfModules.</b>
What I would do if there were no significant difference between the means for
the <b>intentionpre</b>, would be:
<i>aov(intention~constrats*NumberOfModules+Error(Email/constrats),
gdataframe)</i>
What I was thinking to do is adding a column with 
<b>IntentionPre</b> (duplicated for every pre and post value for the
<b>Intention</b> column) and running it like:
<i>aov(intention~intentionPre +
constrats*NumberOfModules+Error(Email/constrats), gdataframe)</i>
Is that a correct reasoning?
Any help would be great!!

Camilo V 		 	   		  
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