I don't know Debian but if their prebuilt kernels are very recent they are usually "back ported" with fixes from newer kernels.
However if you want to compile from the raw source from kernel.org you will have to compile it yourself. This has the benefit of allowing you to customize it for your machine, only compiling the parts you really need and other goodies and options you might want. The prebuilt kernels from distros are more generic so they will work on a variety of machines and CPUs. Custom built ones are leaner and meaner.
So yes, building the kernel yourself can be 686SMP specific if you choose the right options during the build. It can be a daunting process at first but worth learning. Google for tons of help files and documents about doing this. the 2.6 versions use a more streamlined process than older versions so don't be put off by instructions for the older versions.