I don't know if this is an Access XP problem or an Excel XP problem, and I've never discovered an actual, meaningful bug before, but I'm pretty sure I've found one now. I'm going to search for the method to report it to Microsoft but wanted to run it by you to see if anyone has encountered it.
If you're working in Access with a simple select query containing numbers (mine are Long Int.), and you do a copy and paste of all the data in the query result to a blank Excel worksheet, Excel does something weird with the numbers. Formulas and functions don't work on them, even an AutoSum at the bottom of the column doesn't work, but if you add two cells together in a simple formula you'll get the correct result. I've attached a spreadsheet with my query results to illustrate. If you use Access' "Analyze it with Microsoft Excel" button it works just fine, but the copy and paste method is what my folks are used to and we just moved them from 97 to XP and they're really sorry to see their preferred method no longer working.
If you've got any helpful advice about how to report a bug, or if this is old news already, please let me know.