If you have Nikon AF lenses already, the D100 (or fuji S2) is surely a more
sensible buy than the Canon 10D.
Llet's get this into perspective, sure there are 'differences' between the
various dslr's, but the differences aren't all one way and they are mostly of
the same order of magnitude as the 'hair splitting' comparisons between (say)
Nikon and Canon lenses (both are usually superb, and sample to sample variation
probably means that it some cases it comes down to which individual examples of
a lens are tested)
..
If you don't have *any* financial commitment to either Canon or Nikon gear,
then you probably ought to also consider the Olympus E series dslr too, but if
you have any legacy gear just buy the dslr that slots into the system and get
on with enjoying taking photos with it

.
ALL the dslr's are so good performance wise, picking between them on that
criterion alone is a pretty academic balancing off act.
lens wise, if you are using NIKON or FUJI, the Nikon 28-105 f3.5/4.5 is a very
capable lens and makes a nicely balanced companion to a D100 or S2 and is
reasonably priced too, especially compared to the (faster admittedly) AFS
lenses.
Opinion based on my 30+ years as a photographer, many of them spent also
selling cameras of all makes and formats.
>> Stay informed about: canon 10d