For laptops, there's usually no way to upgrade the graphics chipset.
The chips are likely soldered directly to the motherboard. Only high end custom gaming systems have interchangeable graphics chips, and even then, the small market means astronomical prices.

HP Media Center machine
MOBO: ASUS OEM board
CPU: 2.6 GHz Socket AM2 Athlon X2 5000+
RAM: 2 GB Qimonda PC2-4200 DDR2 RAM
GFX: Sapphire Radeon HD 4850
HDD: Seagate Barracuda 320 GB SATA 7200 RPM