Is the Sigma 70-300mm DG Macro For Nikon compatiable with my Nikon D3100?

I have a nikon D3100 and I like the sound of this lens for an amateur photographer, the only problem is it doesn't exactly state what it is or isn't compatible with, I read a few reviews and some say it works with there D3100 and other say it doesn't.
The one i want is this one here -
http://www.amazon.co.uk/...0012X43P2/

It will certainly fit and allow all of your exposure modes.

The problem lies in the presence or absence of a motor, which the D3100 needs because it doesn't have one built into the body.

I know that the 55-200 has a built-in motor, but you'll just have to ask for the motor version of this one (I believe there are motor- and non-motor versions, hence the confusion).

http://www.warehouseexpress.com/buy-sigma-50-200mm-f4-5-6-dc-optical-stabiliser-hsm-nikon-fit/p1031

OS is Sigma's equivalent of Nikon's VR and HSM means it has a built-in focus motor.

Tricky to say from this information. Sigma made this lens in a version without motor but that has been out of production for about 2 years now. They now have this version http://www.sigmaphoto.com/...ized-nikon which has a motor and will be fully compatible with your D3100. From that amazon page it's impossible to say which version it is.

I'd say order it and return it if it turns out to be unmotorized.

Even so, it's not the world's greatest lens. If you're not looking to shoot wildlife or birds then this lens would be a better choice: http://www.amazon.co.uk/...B000O161X0

Not a very good lens I don't think.

Nikon and Tamron make high end, more expensive version 70-300mm lenses that are reputed to be sharp, and have vibration reduction and hypersonic motors. They, and Sigma, also make cheaper grade 70-300mm lenses, and those include the one you are looking at.
If you want a telephoto zoom at about this price level, I agree that the Nikon 55-200mm AF-S VR would be a better buy.

Yes it is compatible with your camera.