Your gear list says you have a Nikon D50 and an 18-55 kit lens. So you should be able to see how a kit lens works for portraits already. They are OK, but only if you have a lot of light and don't need a terribly blurred background.
Can I ask why you are straddling two systems if you are on a limited budget? IT only makes it that much harder to put together a good kit. I think it is time to pick one or the other and get more or less a 18-55 IS/VR, 55-200/250 VR/IS and a 50mm f1.8. THat gives you standard zoom and telephoto with stabilization, and a short, fast portrait prime. Very versatile kit which should come in under $500 on either system. Sell all the lenses you have now and start with some newer, better lenses.