To classify your states by percentages, join the states layer in ArcMap to either a DBF, Excel file or Access table based on either the state FIPS (make sure your table has the FIPS in a text format) or the state abbreviation. If you right click the layer, choose the "Join" option, join based on table attributes.
You then have your table of data "linked" to your states layer, and can classify based on any value, or percentage range you like.
etownsen: If you're using ArcView 9.2 it does read .xls files just like a DBF, or Access file. I would convert your ascii to a DBF or import it to MS Access though. Using Access, it will link the table in but you can't select the data in the table if using x, y point data. To be able to select the point data, link it in from access and then export it to a shapefile. If you bring the data in from a DBF or Excel you can select it. I prefer working with DBFs when using point layers because you can select the data, and when you update the source table (keeping the file name the same) it updates on the fly in ArcView.