Hi scd5394! A kernel is kind of a link between the physical hardware (processor, RAM, etc.) and the applications that run on your phone. Kernels can increase battery life by causing your phone to use a lower voltage and they can make your phone more responsive by overclocking the processor to run faster than its stock speed among other things. IMO, there are very few risks with trying different kernels. Some of them will work fine with your phone and some will never even completely boot in the first place. Perhaps the biggest "risk" is that you will overclock your phone and it will run too hot. When this happens, your phone will typically just reboot...so random reboots can be a sign that the kernel is not quite right for your phone.
There are several developers who have different kernels out there to run with Froyo. Please read the developer's description of what the kernel does and who it is for before you flash it (some only work with Sense). If a kernel isn't to your liking, all you do is flash to another one. It's really that easy.