Check out this technote:
http://www.symantec.com/business/support/index?page=content&id=TECH130961&locale=en_US
Look for the Ghost command line switch "-SPLIT" - this allows you to specify the size of each backup file up to a maximum of 2048 MB.
2048 MB is the default when saving to a network location (as the type of file system cannot be established remotely), or to a FAT or FAT32 partition. When saving to NTFS, the default is one large partition unless you set the -SPLIT parameter on the Ghost command line