Are some Nikkor lenses incompatible with Nikon D5100?

I've read that Nikon D5100 is not compatible with some Nikkor lenses unlike D7000. What are those lenses? Is D5100 a good alternative to D7000 for those on budget?

All currently made Nikkors will be compatible, but there are some that will not autofocus with the D5100 but would autofocus with the D7000. Those are the AF-D lenses which have no built-in autofocus motor and depend on a mechanical link to a motor in the camera body. There are increasing AF-S models available that have their own motors and can autofocus with the D5100. The AF-D models have the virtue of being compatible with many Nikon film cameras, which may not matter to you. Some AF-D prime focus lenses have the nice feature of being easy to dial to infinity in very, very low light.

It's compatible with all post 1960's Nikon lenses - in terms of they'll fit. What it actually means is that the D5100 (and lower models) does not have a focus motor in the camera body, so if you want autofocusing, you have to buy a lens with a focus motor in it - that means lenses marked AF-S (Nikon) or HSM (Sigma).

You can mount AF lenses, but will need to focus manually, metering will still work.

Older lenses still may not meter correctly as well as not auto focusing, so you will need to meter separately as well.