As ZLim noted, both Acronis‘ Disk Director and Symantec‘s (formerly PowerQuest) PartitionMagic will merge multiple partitions. Another program which does this is Paragon Software‘s Partition Manager.
Before attempting to merge the two partitions you may wish to backup any valuable data so that in the event of a problem you will still have access to the information stored on the hard disk drive.
Current beta test versions of Microsoft Windows Vista require about 10GB of space after installation. While this may increase by the time the operating system is released, I would think it would still install on the hard disk drive with your current partitioning scheme.