I have a radeon hd 2600 pro and an athlon xp 3200+ i went on system requirements lab and it said my cpu didn't match it but my cpu speed did. it said i had 2.2 ghz rated at 3.2 ghz. i also have 1.5 gb of ram.
These days the speed of the processor doesn't matter as much. Most processor run up to roughly 3.5GHz on stock speeds, this is about the same as every generation going back the the Pentium 4. But every new generation has brought about performance increases over its predecessor, but not necessarily speed increases.
Basically, you need to replace your computer. Just upgrading is not enough.