This guy was quite nice to put up ARM cross compilation steps for tcpdump/libpcap. You need a cross-compiler for this setup. I used the openmoko toolchain, since it's easy to setup. You can also use the Android source to do this (I think), but I already had openmoko setup.
I had to edit the tcpdump source to disable IPv6 stuff in one function, where it's not ifdefed out. Here's the diff.
NB: make sure to edit the Makefile for tcpdump and remove the -O2 flag and add the -static flag to the linker (LD_FLAGS += -static). Happy tcpdumping :) Update:
Apparently, Michigan removed my home directory, as I am no longer at the university. However, looks like the Symantec folks wrote up a pretty detailed blog spot about this last year, so you could follow their instructions. I recall the only important part being to be sure to statically link the binary. Good luck!