Using old Sigma AF lenses with new DSLR Canon EOS

Yes.

Yes. Bear in mind that many Canon digital SLRs have a sensor smaller than a frame of 35mm film. This results in the image being cropped, narrowing the field of view and making the lens behave as if it was of a longer focal length.

This lens can work with 5D mark II ?

Canon EOS 500N has an EF lens mount, so all lenses with Canon EF mount will fit. All lenses with MF and EF-S won't fit. If you purchased Sigma 28-70mm f/2.8 EX, then it have EF mount and will fit EOS 500N.

Please visit to:

http://www.sigmaphoto.com/sigma-lens-finder

You may be able to find an adaptor, but I doubt it and you would lose many functions in any case. It could end up that the lens will not auto focus or that it would not meter properly. These adaptors are made so that specialty lenses (such as fisheye or shift lenses) can be mounted on cameras when needed. Your 28-200 would probably be cheaper to by in an EOS mount.

It could Canon, this is one of the edge Canon over other brands. Its versatility on lens mount is better.

You can use a Quantaray lens that fits on a Canon EOS film camera body on any Canon EOS camera body - film or digital. Your choice of EOS camera depends on your budget and your needs.

I recommend starting out with a used or refurbished model - let someone else eat the depreciation on the camera. After you have shot with a digital SLR for a while you will have a much better idea what features matter most for your needs and can make a better decision what new(er) model is the best fit for your money. Obviously you know a bit about photography having used a film EOS camera but there are many things that are different about a digital body. One of the biggest differences is that they come out with a new camera several times a year, and a camera body that is just 2-3 years old will be 2-3 generations old, and worth only a small fraction of the price it sold for new - unlike film bodies that held their value much longer.

All canon EF lenses (and compatibles e.g. Sigma EX) can be used with both analog and digital  EOS-bodies. Depending on the sensor size (usually smaller than a 35 mm negative) a crop-factor due to the smaller field of view must be considered.  Example: Canon EF 50mm/1.8 lens used on a digital EOS (40D, crop factor 1.6) equals a 80mm lens (50mm x 1.6) compared to analog cameras using 35mm film. Some digital EOS-models can also use EF-S lens-series.