Here's how I install kernels:
First I download a few and put them on my SD card. Phones are picky about what kernels they like. So, if it's a Chevy kernel I'd d/l the 1.0ULV, 1.0LV, 1.0MV etc.
After you get some on your SD card, go into ROM Manager and select "Install ROM from SD card"
Find where it is and select it - no need to wipe data/cache, but as always MAKE SURE YOU HAVE A CURRENT BACKUP OF YOU ROM
Now, if everything boots up and looks good, you're done. You may need an app like SetCPU in order set the speeds.
HOWEVER, if you get stuck in a boot loop or stuck on the "M" logo this is where downloading several kernels comes in handy
Simply pull the battery out and wait a few seconds. Put it back in a boot up in recovery (hold down the X button while powering on, blah, blah, blah)
Then select "install zip file" (or however it's worded), scroll down to you stash of kernels and pick a different one.