Calling all helpful PHOTOGRAPHERS

I 'm trying to step up my game just a bit. I have a good eye, but I'm just not getting "POP" I'm looking for in my pics. For the next few months I'm on a limited budget so I have to work with what I have until I can upgrade. Here's what I've bought/been given or gifted:
Nikon D5000
Nikon SB-400
Nikon18-55mm 1:3.5-5.6
Nikon 55-200mm 1:4-5.6
Sigma 28-105mm 1:2.8-4
Cowboy Studio Photo Studio Umbrella Four Continuous Background Lighting Kits 600 Watt Output
1 grayish brown backdrop
1 bluish back backdrop
Aperture 3 photo processing software

I've been working hard at taking my camera off the "auto" setting but again i'm just not getting the right tones and I'm having trouble setting the lighting up to get optimal usage.

Again money is tight so I have to work with what I have, but not so tight that I can't make a few small purchases.

Any suggestions? Any help would be greatly appreciated!

Most continuous lighting systems have a colour cast, use your cameras manual colour balance and a piece of white paper to get that sorted.

If you have some money to invest get a flash meter (they will also read continuous light), put your camera into manual mode set the ISO and shutter speed you want, and set the meter with the same settings. Set the meter to read 'incident' light (a white dome (an 'invercone') goes over the sensor for this). With your light set up, from the subjects position point the meter back at the camera and press the read button, it will tell you (to 1/10th of a stop) the correct exposure, set that into your camera and you'll record All the data there's to record. Digital doesn't have any exposure tolerance as film does, +/- 1/4 of a stop can make a huge difference.

Flash in a studio is far more versatile than continuous light, as you can separately control the ambient and flash content of an image, see this site for all the details.

http://strobist.blogspot.com/2006/02/welcome-to-strobist.html

Look in the 101 Archive of how to use cheap manual flashguns (or your SB400 in manual mode) and cheap radio triggers (the Yongnuo RF-602, around £30.00 for a pair recommended). With this setup you can get any lighting arrangement you want.

Sell 18-55 and SB-400 and get SB-600 instead! Get a cheap lightstand for SB-600 so you can use it off camera and shoot through the umbrella. Also get a reflector. Use custom WB as advised above. Use sb-600 as a key light, use your continious sourses for baclground lighting and use the reflector to bounce some light back onto your subject and you got yourself a simple, but effective setup!