1) Excellent LWN write up on linux porting to 2.6 series
2) Intoduction to 2.6 series threading model.
"The 2.6 Linux kernel introduces a new, improved threading model that is implemented through the NPTL. The adoption of a new threading model has significant implications for developers, system run-time libraries such as the GNU C library (glibc), shared application libraries, and so on. This white paper provides an overview of basic threading concepts, discusses new and existing Linux threading models, and then highlights the sorts of application changes that you might have to make to existing multi-threaded applications in order to enable them to work correctly with NPTL under the 2.6 Linux kernel."
3) Customizing a 2.6 kernel
"Kernel configuration is only the first step in building a new kernel. Once you have configured the kernel, you must compile and install it and any loadable kernel modules that you specified during configuration. This step is straightforward if you are building your kernel on the system where you will execute it, but is more complex when you are compiling for a different target system. For example, when rebuilding the Linux kernel for use in embedded systems, you typically configure your kernel on a desktop system and compile it there using a set of tools known as a cross-compiler. "
4) Migrating device drivers to 2.6
" This white paper highlights the major structural differences between device drivers under the 2.6 kernel and earlier versions of the Linux kernel."
5) Using the 2.6 kernel with your current system
"If you are not using an off-the-shelf Linux distribution based on the 2.6 Linux kernel, you will need to verify that the versions of various packages installed on your Linux system have all of the features required for use with the Linux 2.6 kernel. If sufficiently recent versions of these packages are not installed on your system, you will have to update your system to newer versions of these packages."
6) Migrating 2.4 modules to 2.6 kernel
Step by step procedures for writing new kernel modules.
7) How to upgrade to 2.6 kernel
"The purpose of this document is to provide some helpful tips to readers that currently compile their own 2.4 kernels, but haven't yet made the leap to 2.6."
8) Some more 2.6 kernel related news