If it were reversed, (Snow Leopard partition first) I would suggest using the Disk Utility First Aid partitioning option. It would be a matter of just dragging the partition line to the end of the drive and making it one partition.
However, that's not going to work in your case and it may in fact lead to data loss. The best thing to do is make a Time Machine backup of your Snow Leopard installation. Then boot the machine with your Snow Leopard install DVD and erase the entire drive. Create one partition and format it as HFS+. Proceed with the installation of Snow Leopard. It will ask you if you wish to restore from backup. Reply yes and point it to your Time Machine backup.
It'll take awhile to do the restore but you should be back in business with the entire drive devoted to Snow Leopard.
As an alternative method to the above, you could always purchase the handy program "
iPartition" which will non destructively consolidate the partitions for you. However, even with using iPartition, a backup is highly recommended.
Regards.