Right, after managing to install Vista on my MBP I have realised that 30GB wasn't really enough. So would it be possible for me to either enlarge the existing partition or create a second Windows (NTFS) one?
Resizing isn't an option, so you'd need to ghost your Vista partition, use the Boot Camp utility/installer to restore your previous configuration (how the Mac came, with one partition), and then start the Boot Camp process over again, making a new Windows partition, but bigger this time so you don't run into the same problem.