I am currently running Natty with kernel 2.6.38-8-generic on a VAIO laptop running ATI Mobile Radeon and a Core i5 CPU. I was wondering if it were possible to downgrade from kernel 2.6.38-8 to something earlier that doesn't have the power and battery life regression problems that have been keeping me from using Ubuntu abroad. Any help is appreciated.
Instructions for installing different kernels are described here
I would suggest that you deactivate any ATI driver you may have activated/installed first.
Then install the kernels appropriate to your ubuntu architecture - 32 bit or 64bit.
When booting, you'll need to press SHIFT to display your Grub. You can then select the older kernel to boot with.
Phoronix are reporting that the start of the power regression started with the Maverick kernel (2.6.35) and got considerably worse from there. However, others have found no regression - some even better battery life. So its not a consistent picture for everyone.
Assuming you find a kernel stack that works (e.g. Lucid - 2.6.32) then try activating/installing your ATI driver.
Let us know what you find.