Flash for D3000: Nikon Talk Forum: Digital Photography Review
Thats what I found and that site is plenty deep.
I do however think your shadow problem may be solved by adjusting your exposure and get into your manual (flash section).
I also recommend
http://www.amazon.com/dp/0817439390/...SIN=0817439390
It doesn't cover flash photography but should help in understanding exposure there are books on shooting with a flash. Another thing on the dpreview site is "your" camera review, you can learn alot right there. I hope this helps. goodluck
Chris
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