I've done it on several bikes, a couple 350/450 twins and a sohc4 or two. It is not a hard job at all. I am however by no means an expert. You will need to rent/borrow/steal the proper measuring tool(s) to do the job right. Also a piston ring compressor and a ring install tool is also needed (but they are not expensive).
Once you take out the old pistons make sure to measure the bore and compare it to spec so you will know if the cylinders need bored out and oversized rings are needed. If not have the cylinders honed, before piston/ring install. Don't forget assembly lube and new circlips. I have a friend who works at an engine shop, and I just have had him measure/hone/bore for the price of a six pack, so I really dunno what that stuff runs nowadays. I have re-ringed without a hone (engine was well within spec), but, I figure if I am going to the trouble in an old twin, might as well go the whole nine yards since you gotta pull out the whole darn engine to do it.
Here is a link to a good write up, it has all specs, and everything you need to know about how to make your engine "fresh" again.
http://web.ebscohost.com/serrc/pdf?vid=4&hid=17&sid=97647895-be48-40d1-bef5-3ca31ba9796a%40sessionmgr9
