First of all i am a new user of the beagleboard-xm.
I am running the Kernel 3.0.25 of Angstrom.
I am having trouble with finding these files arch/arm/mach-omap2/board-omap3beagle.c and mux.h in the kernel
And beagle.h in the Uboot.
I have mux.h and mux34xx.h in the mach-omap2 folder
I built the Kernel from the standard angstrom repository, and for some reason i just can find these files.
My main problem is im trying to figure out what is the default state of my pins in the Expansion header, and then i want to be able to enable mux.
Thanks in Advance! 
I had the same problem with the BeagleBone (there it was the file board-am335xevm.c that was missing).
The reason in my case was that that file is only creating during the “patch” task while building the kernel target, and was automatically removed later once the target was completed.
I ran “bitbake virtual/kernel -f -c compile” and then the files were there. I think even “bitbake virtual/kernel -f -c patch” should be enough, so you can then modify the files and run the “bitbake virtual/kernel -c compile” task.
Be careful, though, as completing the kernel target completely removes the files, even if you modified them.
Best wishes,
Hermann