Portrait Photography will require a good camera, some lights and or reflectors and maybe some backdrops. Getting an Advanced camera will not give you the control you will want for portrait work. I do portraits with a Sony a200 and get Great results. To start in at entry level D-SLR...look at the:
Sony a300
Canon XS
Nikon D60
They are slightly higher than your budget but you will not regret the choice. Also BestBuy often have these on sale and with special bundles.
A 15-66mm lens is a type of telephoto lens. There should also be a number for f-stop..such as f/4 – 5.6 (or similar). This lens you be better suited for macro work and floral. It could be used for portrait on the long end (50-66). A good portrait lens would be 18-70mm for indoors and a 35-200mm for out doors.

DvD Camcorders are tricky to edit with. The theory being since it is already a DvD that you go directly from camera to player and watch on TV. If a DvD camcorder has a USB port it is usually for exporting the photos from the memory. One way to get the video on your computer is with DvD Ripping software. There are many programs for this. Some are easy to use but generally they are complicated and take a long time to convert the footage. The easiest way is to get a Dazzle from Pinnacle to capture the footage on a computer. It connects by USB and gives you a Audio Video input to patch your camera into so you can record the footage.

Most cameras will want to use a flash for night time shooting because of the Auto setup in Compact Cameras. Digital-SLR cameras give you the most control in night time and low light shooting conditions. With the ability to add faster lenses (lets more light in), increasing the ISO (Sensitivity of the sensor) and Manual Shutter control (how long you can keep the Shutter open) night shooting becomes easy and fun. You don't have to have a fast lens for night shooting....just increasing the ISO and Shutter length will get really good results too. Google “Low Light Photography” to get tips on this kind of photography.

Well...the Nikon D40 is the smallest Megapixel in the group at 6.1 mp. The D60 bumps up to 10.2 with the same bit depth (color information). The D80 seems to have less features that the D60 with both having the same Megapixels. The D90 comes in with the best features over all. 12.3 Megapixels, 11-area autofocus , better frame rate at 4.5fps (frames per second) vs the others at 3fps. This is needed if you ever do any sports or action photography (including dance photography). Bigger LCD at 3” and higher pixels at 920,000 vs 230,000 and 2.5” on the others. A MUCH sharper image on the screen. Live View composition and brilliant playback of the D90's cinematic-quality 24-fps HD D-Movie mode. The D90 also uses a CMOS sensor which is more energy efficient than the CCD used in the others. This will give you longer battery life.

Based on the specs... the D90 would be the better choice. As a first time D-SLR buyer you might feel you out grow the D40 pretty fast...the D40x will be a little better but you wont outgrow the D90 for a long time.