Didn't do a really big print from the D200 file (or D300) as most are used in electronic form or for prints in magazines / books / catalogs (max. double page spread) by my clients.
But I assume you can get pretty big depending on the kind of paper you use based on the experience I had from a print I made for my GF from one of her shots taken with a Nikon P60 (8mp P&S).
I had a panorama printed on canvas at 51.2"x25,6 (130cm x 65 cm) @ 240dpi. That means I upsized the original 3260 x 2450 ppi file, which is approx. 13.6"x10.2" (34.5cm x 26cm) @ 240 dpi, by a factor of 3.8 using Photoshop CS4 bicubic smoother option. The resulting print looks just stunning from 2-3 feet or further away. Getting closer you of course will start to see the limits of the original file quality used. But normal viewing distance for a print in that size will be 5-6 (or even more) feet anyway.
Now, that's on canvas, which of course helps hiding quality issues. But I assume that based on the quality of the D200 files you'll get great results up to about 50" (at the long side) at 300 dpi even on smooth paper (at 240 dpi probably even larger without a big loss in quality), but it will require good preparation of the file and an optimum file to start with.
One thing to remember is that the larger the size, the greater the viewing distance normally is.
Regards,
JH
JH-Pphotography