It's damned near a perfect fit except for the fact that one of the two notches cut into the bottom of the module doesn't line up with the DIMM socket. It's not offset more than a 1/16 of an inch. The other notch lines up perfectly and all the pins are exactly lined up as well.
My thought was that knowing Dell's proclivity for doing little things to make their shit proprietary, this is simply an effort to stop you from using their memory in machines other than their own.
Hey, it was worth asking anyway. I just hate thinking I'm stuck with memory I can't use.
That leaves me with one PC100 128MB module to stick in this board. Not a tragedy, but not what I had hoped for.