T400 - Installing New Drivers Questions

I`m hoping someone can help me out. I have around 2 year old Thinkpad T400 (Windows 7 32 bit) which have been working very good with a few minor issues but yesterday when I turned it on I got a "fan error" at the top left corner and the computer turned off. I opened the case and cleaned out the fan area and made sure the connectors were tight. That did the trick and so far the error has not returned.

Now I thought I should update the notebook, so I installed the latest BIOS (3.23). I have a Ati Mobility Radeon HD 3400 series graphics card with the driver version 8.641.1.1000 released on 8-24-2009, but when I go to Ati site their latest driver 12.4 it states it is not compatible with notebooks with switchable graphics. Is there a more up to date driver that is compatible with my computer? 8.6 seems to be rather old. If I leave it on High Performance permanently would I be able to update to the 12.4 driver? I use my T400 at home only and always plugged in to AC outlet. Is this graphics card powerful enough to play games like Diablo 3?

Thanks for the help.

 

Sorry for the double post. Can mod please delete one.