If anyone is having trouble compiling (no makefiles) or finding (not in the downloaded source) the IEEE 802.15.14 examples that go along with MiXiM like I did, I suggest the following steps:

1. Check out the source using the command

    svn co https://mixim.svn.sourceforge.net/svnroot/mixim mixim

2. Move the contents of the trunk directory into the omnetpp-4.1/samples/MiXiM/ directory
3. Change directories to omnetpp-4.1/samples/MiXiM/examples/ieee802154Narrow
4. Build the project using the command

   opp_makemake -f -O out -L../../out/gcc-debug/base -L../../out/gcc-
   debug/modules -L../../out/gcc-debug/tests/testUtils -lmiximbase -
   lmiximmodules -I../../modules/utility -I../../base/messages -I../../
   base/utils -I../../base/modules -I../../base/phyLayer -o
   ieee802154Narrow

5. Change directories to omnetpp-4.1/samples/MiXiM/examples/ieee802154A
6. Build the project using the command

   opp_makemake -f -O out -L../../out/gcc-debug/base -L../../out/gcc-
   debug/modules -L../../out/gcc-debug/tests/testUtils -lmiximbase -
   lmiximmodules -o ieee8021514a

Now everything should work!