The mega pixels only matter if you are shooting RAW mode. so getting a 10mpx camera doesn[t make a lot of sense if you aren't shooting magazine ads etc. Most photographers don't bother with RAW unless the client specifies it, or unless they have photoshop CS.
Nikon stuff is really expensive, so if you are looking for a bargain, buy the rebel. You can get canon lenses really cheap from second hand stores.
the d-70 is more advanced than the d-100 by the way. and good luck finding used Nikon stuff.

we horde our Nikor lenses etc.