Can I have to Campaigns with the same keywords in them but with a slightly different destination url?
If for testing intentions, you can evenly rotate two different destination URLs within the same ad group across the same set of keywords. If for double-serving intentions, as the previous poster stated - this is not possible.
The main reason's to do this are usually around geographic targeting or ad scheduling where your keywords aren't competing against each other.
If there are searches where more than two keywords could be shown from your account, Google will only show the one with the highest ad rank.
If the above is the objective, like poster_boy suggested, it might be better to have the keyword with 2 different ads (with the different urls) in the same adgroup and then rotate them evenly.