Hi Ian,
I have the 70-300VR and it is a cracking lens. I would imagine that it would be long enough for most things (not knowning the venue at all) and as long as the light is reasonable then you then I can see no reason why it would not be fast enough for what you want :shrug:.
I use mine for birding and even on the D40 I could crop in a reasonable amount without too much loss of IQ - on the D90 you should be able to crop in a bit with no problems.
HTH
Nick
Cool, I think im going to hire one from lensesforhire as its only £30. Havent quite got enough money to go out and buy one yet.
It is a cracking lens for the money - you won't want to hand it back at the end.
You'll need 300mm at the air show due to the flight line. 17-70 will come in handy for the displays.