All DSLR focal lengths are based on Full frame specifications, whether or not it's DX or FX in Nikon context.
Therefore, all DX lenses like for example 55-200mm is actually 82.5 to 300mm (FOV equivalent on FF) on all DX cameras. You still need to mulitply the 1.5 crop factor even though it's a DX lens.
FX lenses are all usuable on DX cameras (1.5 crop factor need to be applied just as well) - but keep in mind that the
D lenses cannot AF on lower end DX bodies due to the lack of motor screw to drive the AF on the lens. Some even older lenses like Ai/AiS can't be metered on lower end DX bodies - but can still be fitted on the bodies and you have to guess the exposure yourself.
Nikon's 70-300 VR while due to really bad CA results, is very sharp nevertheless. Recently bought it for my kid's D5000 and it works really dandy. The results are more impressive than I thought initially.
Tamron's latest 70-300, while better than Nikon's CA control has a different way of handling VR... Some may get used to it, some may not - it's based on personal preferences.
Anyway for better lens comparisons, I'd recommended
www.photozone.de - which is WAAAAAAAAAAAAAAY better than Ken Rockwell's reviews.