There is a handy side by side comparison of the D5000 and the D90 here: http://www.digitalreview.ca/content/Nikon-D5000-D90-Compared-to-Canon-Rebel-T1i-500D.shtml
The D90 is a nice camera and if you can spend the extra I think it is well worth it. It will AF with your older lenses, while the D5000 will not.
Beyond that the D300s is getting more high end.
I have a lot of old F-mount Nikon lenses, and I'd like to get an SLR that can use them. Is the D5000 compatible with the old lenses and, if yes, do all the automatic features like auto-focus work with them.
My eyesight is not as good as when I did film photography, so I also need guidance on the brightness of the screen and viewfinder.
This reminds me, I've heard that some slr's do not show the live scene on the LCD screen--the LCS is only used to review photos. I'd appreciate some clarification.