is manual focus difficult?

[jhamerphoto]

Generally, what everyone has said is perfectly correct, but with the lens you are looking at (very large aperture) you'll have to be even pickier if you want to take advantage of the lens' brightness. A large aperture means a shallower depth of field, so you have to be that much more accurate when focusing.
A little practice, and you should be fine.

My suggestion: wait for the DX version of that lens.

 

[pna]

My suggestion: wait for the DX version of that lens.

I'd even go back to the original advice of picking up a used D80. The rumors of the D90, as well as all of the upgraders that stepped up to the D300 (there seem to be a lot of them in Seattle), is putting a lot of downward pressure on the used D80's. I'm about to pick one up for $550 that has < 7k shots on it and is less than a year old, and there were several that were going for around there. If you can stretch an extra hundred dollars or so from your D40 budget, that would be a great way to go.

I have a feeling the OP is long gone, which always strikes me as funny.