I would suggest not trying to do it. Some say there are two types of concrete, concrete that WILL crack or concrete that IS cracked.
Resurfacing is not necessarily an easy DIY fix. What ever caused the crack in the first place will likely cause the new surface to crack eventually. Oh, and if the resurfacing isn't done correctly then you have a huge mess of that surface flaking off and cracking itself.
If your area is subject to freeze thaws then you might want to get some caulk made for filling cracks in concrete. For a true hairline caulk i wouldn't do anything.
BUT - If you want to create a decorative look. Color it, make it look like flagstone or cobbles or tiles. There are companies that specialize in this and some of the techniques use a resurfacing product. Some techniques just involve staining.
I googled for you and found these guys Pacific Decorative Concrete, Inc. they have a decorative overlay product.