ok,
ATA-100 is a speed rating for IDE disk drives. Basically 100MB/s (IDE drives are also called EIDE)
SATA is different (Serial ATA) Usually marked as SATA-150 (1.5 Gbit/s) or SATA-300 (3.0 Gbit/s)
You basically have to return either the HDD or the Enclosure, there are adaptors, but I wouldn\'t bother because chances are it won\'t fit in an an external drive enclosure.
If you were to buy a SATA HDD it would slide right into that socket you see in your enclosure (one side is the data, the other power).. you don\'t even need that SATA Cable they included.
You basically have an old school HDD and a new school Enclosure. I would say return the HDD if possible and get a SATA.
Just an article that goes into more detail
here