What are the advantages that the Nikon D700, has on the D5100? - 1

? What big differences are there. And what will it effect on my pics?

The D7000 has an AF motor so it can autofocus with AF lenses, not just AF-S lenses
it also has a magnesium alloy body, and to me, is more comfortable than the D5100

they pretty much have the same performance

if you are indeed talking about the full frame D700, then it has a more powerful sensor, better build, and a larger viewfinder, which makes it nicer to shoot. It is overkill for a beginner, however.

The D700 has a full frame (35mm film sized) sensor which gives better noise performance and dynamic range than the APS-C sized sensor in the D5100. The low light performance will be noticeable.

Focus motor in the body so it can auto focus using AF and AF-S lenses.

Full commander flash functionality.

Better build.

Better layout of controls which means you spend less time making adjustments.

Both cameras in a good photographers hands will take wonderful images.
Both cameras in a bad photographers hands will take horrible images.
The D700 will benefit those who have invested time in to the craft of photography.

Edit, I notice that you asked about the next step up from the D5100 and you found out the D7000. The D700 is $2700 for body only (lenses are extra).
The D7000 is $1300 for body only.

The difference between the D7000 and D5100, D7000 has a focus motor in body, better control layout, flash commander mode, and probably better mechanical build. The sensor performance is the same, thus your images will turn out the same.

- Nikon D5000, and former owner of the Nikon D60, I was eager to purchase the D5100 after seeing the announcements and pre-reviews.