The ATI HD 2600 is definitely a substantial upgrade to the 2400. And would certainly be worth it if you regularly exceed the 2400's maximum capabilities.

Unfortunately there is a bit of drama involved. You'll have to update your firmware to get the system to recognize the card. Though that shouldn't be too difficult, as the system should prompt you with the download upon installation.

Otherwise it's nothing that can't be found with a quick google search.

Here's the Guide on how to install your new graphics card if you want it:

Installing iMac Intel 20" EMC 2133 and 2210 Video Card

And good luck.

May I use a pc edition mobility radeon 2400 or 2600 XT? Or I need the mac edition?

Thank you. Luigi

hey guys, can i possibly remove my old graphics card an replace it with a better one cause the one i have sucks like brick, i have an Acer if that matter. an no i dont no how to find out how much my graphics card is...sigh

Hello.

I have replaced 2400XT by 2600XT in my mid 2007 imac. The old graphics card was killed by lightning. I bought this one. http://www.amazon.com/gp/product/B003CO1...

It was actually cheaper then 2400. :)

No firmware upgrades are needed, just plug in and go.