Yes, but Disk Utility greys out (at least used to grey out, I have not checked in a a while) all the options for erasing disk if it is in NTFS format. I had to use a Windows XP machine to partition the external and tell it to keep the first partition in NTFS and the second one FAT32. However, XP puts an artificial limit of 32GB on FAT32 formatted partitions, so I ended up with about four partitions. One NTFS and three FAT32 ones.
Afterwards, I just hooked up my harddisk to my Mac, started Disk Utility and told it to erase two of those FAT32 partitions in HFS+.
If anyone knows an easy way to partition a FAT32 harddisk without a 32GB limit, I am all ears.