Hi! I don't know you, or anything about you, but I DID just spend 30 minutes researching for you...
OK, SO Both cameras are essentially IDENTICAL.
Similar sensor sizes, similar pixel rates. The only real differences that I could find were in the white balance options, which the nikon D90 totally wins, and the screen size and resolution. The D5000 has a 2.7 in with like 250,000 pixels, while D90 boasts 3 in and 910,000 pixels. Nice. The D5000 DOES have two more in-camera editing options, just little effects, but holy cow, who uses those!? I've had my D40 for two years. Not once.
The D90 can save and load camera settings, so one can save and backup settings. Oh what I'd give for that...
The D90 has seriously more options in customizing menus, if you're into that. like 23 to 42. Also, the D90 has about an 850 shot battery, while the D5000 has 510 shots. Pretty serious difference. They're almost exactly the same size, and the D5000 is about 3 oz lighter (more plastic). Oh, also, the D90 shoots just a little bit faster, say, half a second.
In a review by engadget a camera pro stated that the D5000 felt less solid, like I said, more plastic. The D5000 does have a nifty little flip out screen, but only one or two types of shots really need this. I suppose this could be cool for videotaping... Though the central mount that holds the screen on makes me nervous... Imagine it breaking off DDD:
"Now, onto something we weren't so satisfied with: the video mode. As we stressed earlier, it's downright aggravating to think how awesome this 720p video mode would be if the camera could continually autofocus. As it stands, you'll need lots of practice (and lots of coordination) to pull off a video that's devoid of blur. Furthermore, there's still a five minute cap per clip; in case that's not sinking in, you can't shoot movie clips on the D5000 that are longer than five minutes each. Finally, the all-too-familiar "jelly effect" is out in full force here. When taking the camera for a leisurely stroll, our gait alone introduced an unmistakable amount of "wobble," making the video practically useless."
Essentially, you're getting a D90 sensor wrapped in a less sturdy / professional body for a few Benjamins less than Nikon's first DSLR to shoot HD video -- a fair compromise.
Hah... hahahah Only now do I find that the D90 is more expensive. That's life. Best of luck. I just busted my ass avoiding real work. Cheers!
I have a bit of advice. if you can afford about $1300 USD then go with the Nikon D90. It's a VERY good camera if you can pay the price. On the other hand you have the D5000. Has a swivel screen and video. but more in the $700 USD range. I chose between the D3000 and the D5000 when I bought my Nikon. I chose the D3000 cause of the price and the weight of the camera. I also put into consideration the swivel screen might break and that the D3000 was lighter and easier to use for the first time DSLR user (and I am). But for quality of photos and mobility I would say the D90, but expect to spend a lot of moolah. If you want to go cheaper and still get pretty good quality shots then go with the D5000. I would also recommend doing more research. You can go to bestbuy.com and look up cusomer reviews. They also have examples. OR you can just look up the groups here ^^ check out works that have been submited with very little edits and go from there. BUT make sure that they used the factory lense. lenses can alter the quality of shots. I'm no expert but this is my view! hope I helped!