House of Help have taken a look at the Radeon 7500 GFX card from ATi. Heres a snip:
Basically, a Radeon 7500 is a die shrunk and overclocked Radeon, with faster RAM to round out the package. The original Radeon was made on a 0.18 micron process, while the Radeon 7500 is manufactured on a 0.15 micron process. This (and likely other improvements in ATi's manufacturing process, given the large jump in clock speed) allows the Radeon 7500 to be clocked much higher than it's little brother was.