While you can create custom table styles in Excel 2007, I dont think you can apply distinct "header style" to first 2 rows. However, you might consider using some conditional formatting which will specify that if it the first 2 rows in the Table/ListObject it will be formatted in a certain way. That said, it might non-trivial express this requirement in a formula for conditional formatting.
I hope this helps!
Thanks,
Nikhil