This is all really hard to explain via typing...bc it gets really hard to explain what happens visually. But, the kit lens w/ the D5000 is an 18-55mm lens...just basic, nothing special - not a lens you'd really go out and buy on its own, per se. It will totally fine to learn on though, and figure things out with etcetera. That's why some people will say, just buy the camera body alone, and then get the lenses you really *want*. Skip the kit lens.
Depends on BrowniesMom's lens...I'd see what she likes/dislikes. It's a nice lens. But, bc it's a Macro, it may be tough to use w/ the doggies bc if they move, *boom*, they're out of focus. That said, a Macro Zoom would be a super fun lens. You'd need to know if this lens has its own motor (I think with sigma lenses, this is designated by HFS or HFX or something like that?) (in Nikon lenses, you look for AFS lenses if you need the motor IN the lens).
It depends...do I have the right info regarding the D60? I was under the impression that the D60 was similar to the D40 in that it doesn't have an in-body focus motor -- is that correct? If it does *not*, then the 50mm could still be used on the D40/60, but would not auto focus -- you'd be stuck w/ manual focus.
No, the D5000 is not the same as the D40/60, def. not...I probably confused you, sorry. The D5000 is still beyond the D60 -- I mean, it has almost all that the D90 has, except for the movie quality and the focus motor issue.
Another option would be to buy a used D80....a great camera...but I don't actually know if it does video or not.
I'm sorry if this is confusing...but it really *is* this confusing when you're trying to buy a camera. Been there! 