How to enable usbmon?

[Pasha R]

I need to perform some USB sniffing with usbmon. I'm trying to follow
instructions in file
/usr/share/doc/kernel-doc-2.6.23/Documentation/usb/usbmon.txt. But,
when I get to 'modprobe usbmon' it can't find the kernel module. Is
there a way to compile it without rebuilding the whole kernel? Also,
where can I find documentation on how to recompile kernel SRPM? It
looks like when I try to build it, the build system overwrites my
config file.