PBase

Dear Moderators,
Please kindly give me some ideas on taking good portrait photos at low lighting condition using Nikon D40x , Nikon 18-200mm VR lens and flash unit SB600. In the past I used Nikon F80 , filem ISO 400, Nikon 50mm 1.8D and nikon flash unit SB26. The photos were sharp. Now I am learning to use DSLR camera. I like to use manual mode when taking photos. Please guide me. I thank you.

First of all I am not a Nikon user I use a Canon but I am pretty sure that the capabilities would be similar, if you are in low light increase the ISO to a level that gives the result that you want, just like the film days using ISO400 increase the ISO on you dslr to a similar level and see if the results improve.
Read you manual on how to do this....
See if that helps at all...

I have a Canon 350d and used a Tamron 18-200 on a 6 week tour through Europe and found I could overexpose a hand held shot in low light indoor shots so yours should be similar...