I'm interested in compiling a 2.6.x kernel, is this is a decent guide?
 

Ubuntu Hoary comes with 2.6.10.

For kicks (aka the heck of it), I'd like to compile 2.6.12.3. I'm on 56K, so I downloaded this older version a month ago.

Is this a good guide?

Or is this better?

The second guide looks better, read it through before you start. If you have problems, 9/10 you've made a bad selection during the configuration.
Not many succeed the first time they do a custom compile, but if you keep trying and you manage to make a good configuration, it is certainly worth the trouble.
btw. once you have a good configuration, save it for later, it is in the .config file in the /usr/src/linux directory, but I expect the guide to tell you all about that ;).

greetings,
elluva

A good tutorial for compiling kernels on debian and debian based distros is here:

http://newbiedoc.sourceforge.net/system/kernel-pkg.html

Can I use my old configuration (ie. the one I have for 2.6.10) for this new kernel compile?

Is that what oldconfig means?

you can use the config with the stock kernel if you like, but it is better and more educational to at least adjust it so that you do not compile stuff you do not need. oldconfig is a method of picking options like menuconfig, xconfig, or gconfig. I think most people think of it as deprecated. menuconfig is the all-around best option.

Yes, you can probably retrieve it in /boot/config-*. You just copy it to /usr/src/linux/.config and run 'make oldconfig' from that directory. It is possible to retrieve your config by the proc filesystem as well, but this functionality has to be compiled in the kernel (I think it is /proc/sys/kernel/config or something).

yes.

There's nothing wrong with using an oldconfig IF I am not interested in using any new features, right?

There is never something wrong with using oldconfig, since you'll be prompted with the new features available ;). btw. you can just copy an old config into the /usr/src/linux dir and then use menuconfig as well. The old configuration will appear in the menu's as well, but the new options will be marked (NEW).