OpenGL 2.0 issues with an upgraded Dimension 2400

OK,  Teaching my son about computers with his grandfathers old Dimension 2400, running XP 32 Bit.

We have upgraded the CPU: Intel P4 3.06 GHz

We have maxed out the Ram: 2GB

He plays Minecraft, so we got a ATI Radeon 7000 video card, installed it today, updated the drivers. (disabled the onboard graphics) restarted repeatedly.

We have the latest Java.

Minecraft keeps saying that the graphics card is outdated, OpenGL 2.0 is soon to be the standard minimum.

Is there any way to get the Radeon to comply?

I'm weak on computer jargon, so give it to me in layman terms. Thanks!