thanks bro...
dude I suggest just investing in the overhead flash. if you get the D80 you still need either the SB600 or the SB-R200 and for these flashes to work wireless you need to use the built in flash to trigger the remote flashes there's no way around it believe me I called nikon tech support on this...
anyway like some of the guys here had suggested to cover the built in flash with something; Well I really didnt want to rig something up and it was too much of a hassle so I just purchased the SU800 speedlight commander; just alot easier...
Mike that's all you need... you dont need a new camera; you just need a remote flash that would sit on top or your tank while you take pix. I turn off all the lights in the room and take pix with just the flash...
Plus it's also gonna cost you around $500 for both commander and speedlight unless you buy used or unless you want to rig something for the built in flash; then all you'll need is the speedlight....but GL with it bro...