how can i get my photos like this?

[fakename123]

i have a nikon d70 and a external flash with it

i want to achieve effects like this:
+ http://www.hobogestapo.com/galleries.cfm?id=810
+ http://www.hobogestapo.com/galleries.cfm?id=781

i can tell a couple of photos have vignetting, but also find that some shots in the middle the flash is really obvious

help?? tips?? thoughts??

[ofnuts]

From the shadows, the flash must have been rather far from the lens axis, likely a cobra flash shooting vertically up with a 45° reflector on top or a Gary Fong diffuser.

Vignetting can be "natural" with flash. If the outer elements are farther than the subject they reflect less light and appear darker. You can also use a "snoot" to focus the flash beam.