I am planning on getting a digital SLR, prob either a Nikon d80 or d40. I will only ever be viewing these images on a 26" / 30" (someday maybe bigger) LCD monitor for work. Will there be any substantial difference in image quality between the d40 6mp and the d80 10mp image when viewed on LCD monitor? I can't imagine that I would be cropping on the screen more than 50-75%. Does 4mp make that big a difference when only ever screen viewing on a 26" or larger LCD?

On your monitor no. The difference is not so much in the megapixels but rather in the quality of the sensor (tech in the sensor) and the image processor. Depending on what you need the D40 will suffice. If all you need are some basic pictures on your monitor the D40 will do. Your monitor only requires 2MP or so for 100% viewing. The D80 will in general provide cleaner noise free images (if you want iso performance better than 1600 with no noise you'll need a D300 :D) and better colour rendition. Try them out with your own cards at a store and compare!

Good idea with trying my own cards in the shop, I wouldn't have thought of that. Thanks.

I agree that it really won't make any difference between the two just comparing image files on a monitor. Check the monitor's resolution - I highly doubt that even one that big will display six million pixels. But good advice about trying out with your own card just to be sure.

The highest resolution monitors generally available are the high quality 30" displays from Apple, Dell, and a few others, all well over $1000, which will display 2560x1600 pixels, about 4mp, which is still less than the 3008x2000 pixels you'll get from a 6mp Nikon. Most good widescreen displays out there are 1920x1200 or less, depending on size: usually 1440x900 or 1680x1050 for 22" or less, 1920x1200 for 23" and larger. 1920x1200 is just a bit over 2 megapixels.