Well, if you take a tour of the paint/wood stain aisle of your home improvement store, you'll find plenty of different strippers. (chemical strippers, that is. lol) One of the non-toxic strippers is called CitriStrip (brand name). You apply these compounds to the wood (either brush or rub on with a cloth). Wear thick rubber gloves! You wait, then scrape off the paint or varnish.
(You can also use a heat gun to remove old paint. It hasn't worked well for me, though.)
It sounds from your description that your cabinets are stained. In this case, you would use a stripper, then use a wood bleach like Henry described in his last message. Read it carefully--it contains a lot of info.
Lastly, plan on getting messy. Protect floors, etc. This has just been my experience with stripping paint and varnish.