I have the Nikor 70-300 G series lens, and it is their cheapest lens.  I'd
go for the VR series lenses, and you'll find out it is out of stock in a lot
of places.  The VR lens is compatible with the D50.

I've got the ED version and really like it.  So do some folks on flickr.com
where there's lots of examples posted.  It is fashionable to knock the Nikon
70300 G and ED.  Maybe I just got a good one.

I have a  80-200  2.8  and a 70-300 4-5.6 D  ED   not  the G
  I  always  take  the  80- 200  first  it is  superb

Out of the three models Nikon offers, the new 70-300 VR lense appears to
be superior to the other two older models across the zoom range. It's
not as good as the pro lenses obviously, but it is quite good even at
the long end where the older models were rather soft:

http://www.filmlives.net/community/viewtopic.php?t=812

The addition of VR to the better optics is a nice bonus, especially for
handheld shots at 200-300mm. I think Nikon has another winner with this
lense.

About 5 years ago I bought the Nikon 70-300mm f/4-5.6D ED lens and I've been
quite happy with the images I've gotten, both on the D70 and (mostly) ISO
100-200 negative film with D90 and F100 cameras.  Sure there are better, but
they're also quite a bit more expensive.  Unless you need real action shots
(i.e. f/2.8) or immense enlargements, you can't go really wrong with the ED.

   Norm

Unless you are disciplined about using a tripod, I expect you will see
dramatically better results with the VR lens than with any of the others you
mentioned.  Whether it's worth the extra cost is up to you :-)

The Nikkor 70-300mm f/4.5-5.6G VR you mention will work perfectly on your
D50 or any other recent Nikon. I got one just recently and it works fine on
both my D70s and D40.

It's the D40, not the D50, that has problems with some slightly older Nikon
AF lenses. That's because the D40 doesn't have the "screwdriver" autofocus
connection in the camera body for those lenses; it requires a lens with the
AF motor built into the lens itself. That's not an issue with the D50 since
it does have that connection, and it's not an issue with the 70-300 VR lens
anyway since it does have the (SWM) motor built in -- which is what your D50
will use with that lens.

And it's one magnificent lens, by the way. Well worth the $530, though you
may have to wait a while to get it for that. I got my order in early at
Camera World at that price and got the lens in a couple of months, but I
notice that some other sellers are getting $590 for it right now.

Neil