It has an "F" lens mount. source: http://www.dpreview.com/reviews/nikond50/page5.asp
and nikon camera can use a nikon lens, try a D3000, a D50, or a D9
Yes
Yes as long as it's not pre AI
The Nikon D50 digital camera costs $1899.66 at Amazon. Yahoo sell it for much less at $599, eBay sell it the same price as Yahoo, but body only without lens.
Yes, it will fit. However, you will still need to see if the lens you have has or does not have features like autofocus or CPU connectors that will carry all the info that your camera needs... If it is a Nikon Lens it will work fine. So will others like Sigma, Tamron and Tokina. Carl Zeiss may not give you all the functions but will work in manual mode.
Most Nikon lens will work in complete manual mode, but to get the most from the lens (auto-focus, metering) stick to Nikkor lenses with AF or G in the title. Full comparability chart in the related links below.
Read the user guide
Yes, pre AI lenses may cause damage though
no, you would have to get a nikon module
Yes but older AF lenses that do not have an autofocus motor in them will not autofocus with the D5000.
The nikon D40 camera is an entry level model in the nikon line up of digital SLR's. It was made with the the intention of capturing an audience of consumers that would conventionally purchase a point and shoot camera. In other words this camera was not designed for rigorous and serious photography, hence the reason for its short battery power. As a matter of fact you may notice that the battery life of a D40 actually is shorter than a comparable point and shoot camera. This is because the battery nikon used in the D40 has the same "lithium strength" as most high end point shoot cameras but will perform more battery draining functions because it is in essence an SLR. The D50's, D70's etc were not designed for the same consumer market as the D40. If you compare these cameras to the D40 you will notice they are physically bigger, have a stronger built quality, they have a top LCD etc. all to show that these cameras were made for an amateur photographer market as opposed to the point and shoot consumer. Furthermore, batteries that are used in higher end cameras like the D80 and D200 can also be used in a D50 but not in a D40. Further showing that the D40 is rather like a 'stepchild' in the nikon DSLR family, than a bona fide nikon DSLR. There are other issues like lens compatibility that are a problem with the D40 when compared with its bigger siblings.
Nikon specifically states that the D50 can only accommodate up to a 2GB SD card. However, some users find they can use the 4GB card with their D50s (see Resources). Although not guaranteed, use only SDSC and not SDHC (High-Capacity) cards.