My understanding of how modules are built in 2.6 kernels and definetly from my experience the user building modules needs write access to the kernel source tree to be able to build modules succesfully. and your errors are consistent with what i have experienced the only way as a user to build is to change the owner to yourself of the tree or give all write access to the tree
2.6 kernel modules DO NOT NEED the kernel source in order to build. The headers supplied in /lib/modules/VERSION/build/include are generally all kernel modules need to build against. In most cases a module needs fixing if it does not live up to this rule, or maybe just the build procedure.
Warren
