I recently purchased a Nikon D50 with a Tamron 28-80mm and a Tamron 70-300mm lens.
Your sig says you want a D80. Why? You'd still be shooting through those Tamron lenses. If you want better images you should be looking at upgrading the optics first. A couple more megapixels will not make one bit of difference But if you spent just a little on a
used Nikon macro lens. you'd see a dramatic improvement. basically night and day level of difference in result.
I have a 30 year old Nikon macro lens that is absolutely tack sharp. You can pick these up for under $100. If you do decide to get one the autofocus lenses are nice but if you don't have the cash look for an "AI-S" type manual focus lens. These older "Micro Nikors" are still among the best ever made and they are cheap on today's used market
I assume you are using a tripod for this type of work. If not there is little hope of ever getting a really sharp image. Small movements in and out of a few millimeters throw off the focus. You need to keep the camera from moving. If you don't have and can't afford a tripod use a ziplock bag filled with sand on top of a stack of cinder blocks as a camera suport ($5 total cost) Also use the IR remote control to trip the shutter so your finger does not shake the camera. If you don't have the remove then you can use the self timer. Set a 10 second delay to give the camera time to stop shaking. But if outdoors you want to trip the shutter just as the wind stops, and as luck would have it, if using the timer a puff of wind always comes up. The remote let's you pick the exact time. Worth $19.95.
One other thing. If these are for the web. Don't down sample, crop instead. Pull the camera back three feet then crop of the tiny flower from the center of the frame. If all you need is a 300 pixel image this works best and aviods the whole issue of macro photography
