Sue, I second Mark's recommendation that you choose Canon and take a look at
the Rebel XTi.  Nature photographers seem to prefer the Canons and I have
heard really good things about the latest Rebel Camera.  If you want to go
semi-pro, then the 30D is the latest, but I warn you that it is likely to be
replaced in the near future: these things cycle every two years or so.  On
the other hand, you can get some good deals when the marketers know the
model is getting a little long in the tooth.  You won't go wrong with either
and you will have wide choice of lenses.  At 10.2 the XTi has more megapixel
depth than the 30D in fact.  If a got a camera today, knowing what I know, I
wouldn't buy one with less than 10.  The 30D is 8.2, which is considered the
very least needed for good strong prints.  The XTi body only is going around
$500 body only, while the 30D is now $730ish, much lower than when it first
came out.  For anything better in the Canon range you will have to spend
$2000+.  At this juncture I would recommend the XTi, and then advise you to
spend whatever else you have budgeted on the lenses.  These are going to be
the most important part of your system going into the future.  

Sorry to be so long-winded; let us know if you have additional
questions...on or off list.

Happy shopping,

Fran Saunders
Cambridge, MD