TS - since u have some old nikon lense, check if the glasses are still in good condition, if so u can consider staying with nikon and pick up a D80/90. D80 is discon but still can find some 1st hand at some shops.
D80 is a good camera to use and easy to pickup in terms of usage, D90 is a notch better than the D80 with its LCD and ISO performance. good up to ISO 1600 and the 3" LCD is sharper and better, allow u to review your shoots on the spot better, checking for sharpness and color. D80's LCD cant show purple well from my experiance, D90 from my friend show purple much better.
Side track: (what i know, but i may be wrong so pls correct me if so. more knowledge )
Nikon lens some dont have build in focus motor but all lense be it old or new can be mounted onto any Nikon camera FX or DX or old film type and use.
Canon got EF and EF-S lens and all have build in focusing motor but EF-S lens cant be mounted onto a full frame camera as it will damage the camera flip up mirror.