17-55 f 2.8 or 24-70 f2.8?

Hi,

I'm currently using a D5000 with 18-200mm f3.5-5.6 Nikkor. I'm thinking of investing to upgrade by adding either a AF-S DX Zoom-Nikkor 17-55mm f/2.8G IF-ED or a AF-S NIKKOR 24-70mm f/2.8G ED.

I plan to use it mainly in nature/cities for hobby purposes, and don't want to upgrade to FX body in near future. The questions I have are:

• would both lenses work with autofocus on the D5000?

• which one is a better choice for a DX? I understood the 24-70 is one of the best lenses of Nikon ever, however on the DX due to crop it's almost the same (in wide angle even worse) than the the 17-55, and also more expensive/bigger

• if 17-55, is it still available? I saw out of stock messages everywhere... is a new model expected?

thanks in advance
Gergely