Validating two sets of controls

I have a web form that contains two sets of controls and one button.  The user needs to set/select values from one set (not both) and click the button to submit the form.  What would be the best way to validate their selections/input using the validation controls?  I was going to use a custom validator to check for the presence of a value in either set, but can you couple that with the other validation controls for each input control?
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