The software Ric is telling you about will help you resize the partition. I've personally never used this software, but have used Partition Magic (which runs on the Windoze partition) with mixed results.
This software will allow you to repartion the Windoze partition to what you would like, but I have to warn you. BootCamp is still in beta and is very picky when it comes to messing with things it controls like the partition size. So, make sure you backup your stuff before attempting it no matter what software or way you choose...cause it's a very good possiblity that you may hose your Windoze partition and you will have to do what Ric first mentioned in using the BootCamp Assistant to resize your partition.