How do you level 1/2" x 6" flooring planks?
If your subfloor is only a 1/2 inch thick and partially rotten you need to replace it. Even if it were in perfect condition that's not thick enough for laminate flooring, it will droop and bounce like walking on sponge cake. Cut out your floor boards, true up/replace/sister your floor joists using a site laser or string line and power plane if they need it (and I'd bet you a shiny nickel they do)especially if the joists are under the span load limit, here's a tutorial on span limits:
http://www.awc.org/technical/spantables/tutorial.php
It looks daunting but its not as bad as it looks. If you're still fuzzy just go to your local building center and they can usually calculate loads and spans for you. Once you've got that figured out, sheet with 3/4 t&amp;g cdx. Run a bead of PL on the joists to fill and small voids and bind it all together. Here's a pretty thorough link from a sheeting manufacturer. 
http://buildgp.com/wood-products-installation-tips
Hope this helps!