This gives a quick way of being able to load an XML file. You can then use the standard MS DOMDocument methods and properties to access the data.
You can then use an ADO connection to your Excel sheet and read the records from there. I'd create some sort of ODT class for the data from the Excel record and another one with the data from XML and then write a routine to compare property by property the two objects.
I don't have the code at my fingertips right here for it but hopefully my suggestions give you a starting point.
Re: How to fetch data from an XMl file and comp eXcel
Additionally to Robert's suggestions, you can find information on working with XML files in the "Working With XML Files From Scripts" help topic.
As for Excel files, you can use the Data-Driven Testing feature to read them (see the "Data-Driven Testing" help topic).