To clarify the above, >>6447 is correct in that you can't take the dowry without taking the princess, unless you have the encrusted chest from Dragon Princess I. And if you do, you CAN get up to five dowries, but without later-generation shenanigans two of them must be the Encrusted Chest (which allows you to swap princesses for dowries) and the Draconic Ruby (from swapping out Dragon Princess I herself, as you must save her to get the chest).
However, if you're willing to wait until generation 3, you can take four princesses with dowries you want, wait a while, and then get Wizard Master (able to switch out any dowry for another). You then get him to turn the free-be dowry you have to get from the first princess into the encrusted chest, and then you can turn the four princesses into the dowries you wanted. For added fun, if you get the wealth bonus of Rabbit Princess (also generation 3) you can gain an additional dowry from one of those four princesses, for a total of five (and the chest) without having to have any of the Gen 1 princesses.
…actually, thinking about it, it'd be better (in terms of final dowries) to just rescue Dragon Princess I, swap her for the ruby, and then later use Wizard Master to swap the chest out for any other dowry you want. This still lets you get four separate dowries that you want, AND leaves you with the superior Draconic Ruby rather than the by then useless Encrusted Chest. …unless you go by an interpretation of the rules where you can swap dowries back out for princesses, in which case your mileage may vary.
As a last piece of info, Gen 3 added end-game rewards based on the princesses you rescued over the course of the game, and what you did with them and their dowries/idols/lust-gifts… two of which give you additional Wagon Slots if you voluntarily choose to skip 1-2 generations. Therefore, if you didn't want to do generation 2, or 3, you could gain up to 2 more potential dowries, for a grand possible total of 8 (five from the normal gen 1 slots, two more from the reward, and then 1 from either the reward or rabbit princess, depending on whether you did gen 3).
Info-dump over. Probably more information than you wanted, but I try to be thorough. :3