Possibly not something to try if you're not feeling brave and/or knowledgeable, but in most cases (based on my experiences, at least) configuring a kernel extracts the config of the currently running kernel and uses that as a base if there is no pre-existing .config file.
That is, if you execute the following (assuming you have your new sources in /usr/src/linux):
# cd /usr/src/linux
# make mrproper
# make menuconfig (or 'make xconfig' if you prefer)
then the default already selected options will be those that match your running kernel as closely as possible. Saving the config, exiting, and a make bzImage && make modules && make modules_install && make install should
build you a kernel of the desired version with the same functionality of your existing kernel.
Of course, there's a chance I'm wrong for your particular setup and it'll build you a kernel that won't recognise your graphics card or netword card or modem, etc. But so long as you check all the options first, you should be OK. Building kernels isn't as scary or hard as you'd think it would be.