You can just upgrade the kernel using apt, it takes care of adding it to grub and all of that too, and the latest one you have installed I believe becomes the default in grub as well (grub is the boot loader btw). So all you need to do is a:
apt-get install kernel-image-2.6.8-2-386
Or whatever kernel you need, they have the 2.6.11 kernels available and optimized for other cpus, for example, if you have an athlon xp, you could get the k7 kernel instead of just the 386 one. Also, if you ever need to do things that compile against the kernel, you might want to install the kernel-headers, they're usually called kernel-headers-2.6blahblah, the same suffix as your kernel.
You can use synaptic of course as well, just search for kernel or whatever and you'll find it. It works really well to, upgrading kernels has always been painless this way for me
I was amazed myself how nice it was the first time I did it.
You could always compile your own kernel but it takes a long time, but sometimes you need certain options enabled, but unless that is needed, I find it a bit too troubling and difficult, at least for me.
I'd just go with apt/synaptic.
Edit: forgot to say, just install it with synaptic, then restart your comp and hopefully it will be the new kernel as default in grub, and it will boot up fine and you're good to go. If you use the nvidia drivers those will have to be reinstalled but that's about it.
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