GOT IT!!!
It's an HD 2400. Did a search of the HP Parts Store with this number, 462477-001, and up popped this: Graphics card - 256MB, PCIe (x16), ATI B276 RV610, HD2400
Edit:
There's a trick to getting HP site links to show properly, but I haven't figured it out yet.
Just pop 462477-001 into the "Search by part number" here:
HP Parts Store