Install new kernel on old distros (such as CentOS)

In short, choose YES for one configuration in the new kernel:
General config-->enable deprecated sysfs features which may confuse old userspace tools
(or similar, on 2.6.31.13, it is callled "remove sysfs features that may confuse old userspace tools")

Otherwise, you will get a kernel panic during boot and some errors, like "could not mount root filesystem".

ref: (Chinese version, some explantion about initrd.img.)
http://hi.baidu.com/mhlovejn/blog/item/930c96314f6311f21a4cffc6.html
http://hi.baidu.com/mhlovejn/blog/item/53740d298870c8f0e6cd4095.html
http://hi.baidu.com/mhlovejn/blog/item/7a4a55fe65de7488b801a020.html

Update : 11.4.2011

On kernel 3.0.8 (or some recent versions), this setting becomes a run time option. That means after enable it in the menuconfig, you also need to add one line in the grub, after kernel line, like:

kernel xxxx, sysfs.deprecated=1