What's the highest GPU that this CPU can support?

I've got myself a new laptop and I'm giving out my PC to my little brother. He wants to play some games on it, but the Radeon 4850HD is a very outdated GPU. So I'm asking this - What's the most high-end GPU that this CPU (Athlon 5600+ 2.90GHz) can support, without bottlenecking it?

Unfortunately there's little chance of upgrading the CPU or GPU on a Notebook's motherboard unless such a change was offered as an option by the OEM/Vendor of the Notebook. They just aren't much upgradeable except for the HDD and the RAM, sometimes can go from a CD-ROM/CD-R/CD-RW to a Multi-Format drive.

Berton said:

Unfortunately there's little chance of upgrading the CPU or GPU on a Notebook's motherboard unless such a change was offered as an option by the OEM/Vendor of the Notebook. They just aren't much upgradeable except for the HDD and the RAM, sometimes can go from a CD-ROM/CD-R/CD-RW to a Multi-Format drive.

Um sorry, don't look at those specs. As I said, I got myself a new laptop and now I want to upgrade my older PC.