+1 to those questions - without an idea of what system and what kind of budget you are looking at we can't really give many recommendations.
The only generalist advice I can give is that typically bird photographers say that bird photography starts at 400mm and from there the longer the better.
sorry for the loss of information. Im using a 35mm Minolta Maxxum400si.
No real set price range yet. But the lower the better without getting crappy quality. Im saving up for a D90
It entirely depends on where this bird is located in relation to the camera.
In general the very best thing you can do is get as close as possible to eliminate a bunch of technical problems related to shutter speed and aperture.
a d90 is a good body to start with(i only have a d80). as far as the lense i have no clue but as mentioned before anything less than 400mm is useless. save your money n buy a tamron or sigma to start. quantaray isnt bad either.
BIF's (birds-in-flight) are tough, take good reach, and a good tripod and head.
People who do BIF's seriously - like to use $7000 top-of-the-line pro camera bodies, 600 mm f/4 prime lenses ($10,000 plus) mounted on $600 Wimberly gimbled tripod heads, all setting on top of $900 Gitzo tripods.
I've seen great things done with a sigma 50-500mm and a 40D camera body and no tripod So its not all topflying gear - though it certainly helps to have it for certain and widlife in general is one of the most expensive areas of photography.
That said I'm sad to say I can't give any specific lens suggestions - I don't know your camera range or mount type at all - though a quick google shows that its an older film camera body so you might have luck with some film era glass on ebay - but otherwise I can't give any recommendations.
I hate to be the one to say it, but realistically for someone who is saving for a D90 there's not a lot of options. You would be looking at $2k minimum for a lens that wouldn't even get that much reach (70-200). A 1.7x teleconverter will give it an effective 510mm on a cropped sensor. That brings you to around $2500.
Can you get cheaper lenses with long focal lengths? Sure. Will they be good for catching birds in mid flight? Nope.