The speedlight is the sb600 i think and the lens is the Nikkor 70-300mm. ALSO on a regualr digital camera I know that 400mm = 12x zoom so what would 300mm equal? AND also is the 18 - 55mm wide angle? What will you be using your camera more for? Your requirement depends entirely for that.
Personally I use my zoom lens (Nikon 80-200 2.8) far more than I use my speedlight (SB800).
Nikon D50 is a good camera, but unfortunately, it's failed in the market. Most people prefer to go for the D70/D70s. I used to have the D100 till Jan. Sold it & now am using the D200. I would go with the speed light. You can always buy another lens after you familiarize yourself with your new Nikon, a great camera by the way. http://www.oniva.com/upload/492/Nikon-D5...
try this | 
