D'oh! Sorry about that. You were clear, I just had a brain glitch.
I don't know a way to fix that, but I took a quick look at the ODBC Programmers Reference at msdn, and they're mentioning that the MDAC 2.7 ODBC libraries allow 64-bit values for the SQLLEN data type (used by SQLRowCount). If you're on a Windows platform, it might be sufficient to make sure you're using the latest ODBC libraries. (Of course, the Teradata end might still be using the 32 bit types, in which case you're probably out of luck.)