common regulation - gene list from microarray (Oct/05/2005 )

Hi
I have a list of rat genes as a result of microarray analysis.
I'd like to statistically determine if these genes are under
common regulation (eg, they have common regulatory elements).
If anybody knows about the procedure, please let me know.

Thanks.

I am looking for methods that can detect common cis-acting elements
in a group of about a hundred genes and compare the frequencies of those
elements with those in background genes.

Thanks.