I am a former user of Nikon D50 (and its film SLRs) and a current user of K10D.
I have considered D80 before and I love the viewfinder.
It is very bright, bigger and clearer than D50.
However, it does not have compatibility (metering only
possible in manual mode) to manual focus lenses.
If you are using the kit lens, i think both are quite the same.
Nikon has several cheaper AFS-G lens.
Nikon has a good range of zooms lens.
But Pentax has some of the best fixed lens in the SLR world.
(31,43,77 limited edition)
I feel Nikon's metering is slightly more accurate, Auto white balance is
very handy for no-brainer operation.
But if you like to stick to fundamental, learn the basics, go through
what the old birds had gone through, know what is colour shift in
different lightings, Pentax's white balance is very powerful and
highly configurable. But do prepare to do your homework
when you traverse this path.
Otherwise, adjust the colours during the post processing.
Nikon has better support and choices in second hand market.
Mmmmm, so why do I choose K10D?
Simple....
price, features {shake reduction, weather proof, dust cleaning},
well thought out ergonomics during operation (e.g. green button)
availability of the best fixed lens money can buy.
build quality is slightly better than D80. You need D200 to
fight with K10D.
Yeah Nikon has its fair share of classic lens (105/2.5, 85/1.4, 105/2.8DC, 35/1.4,
180/2.8 ...) but Pentax limited edition range is designed from ground up,
and well executed. One only needs a deep pocket ...

(which I don't have, but aspire to acquire, bit by bit...)
The biggest bang for the buck, K10D cannot be beaten.
But if you forsee yourselves prefering to acquire zoom lens, buy and sell
in second hand market, Nikon is more suitable.
Since you mentioned that you are a new SLR user, I think it is difficult to
visualise where you like to go.
Maybe you preview your gadget acqusition history, and decide from there.
E.g. if you own a car, likes to mod it, buy different parts to tinker....
change handphones every two months...
-> most likely camp in buy n sell
