Want to add 4th drive on a system with just 3 SATA ports

[archeopetrix]

I have Gigabyte GA-G33M-S2H mobo with following features
3x internal SATA II ports
1x eSATA port on the back panel
1x PCI Express x16 slot
1x PCI Express x1 slot

I already have 3 sata drives connected to all three internal SATA ports.
And now I want to connect 4th internal SATA drive (Seagate Barracuda 7200.12).

Can I use eSATA port on the back panel to connect this 4th (internal, Seagate Barracuda) drive ? If yes, then how? Are there eSATA enclosures available which can hold 3.5" Seagate Barracuda internal drives? Do such enclosures require external power source with AC adapter?

Or are there simple eSata cables available that can connect my Internal 3.5" Barracuda to eSata port and let the power source be the normal Sata power rail from PSU. (This i would prefer over the enclosure/case if it exits)

What are Sata port multipliers? Can I use them instead of using eSata port for adding 4th sata drive?? Do these sata port multipliers connect to mother board using PCI Express slot or through one of the 3 onboard SATA ports??

Sorry for the noob question. Any advice would be appreciated. Thanks!

[elex13]

i just giving you answer by just reading your question title. If your motjrboard have any PCI slot then you can add a card named pci to sata card.The card is approx 400rs in indian rupee means about 10 to 15 $.there are almost two to four sata slot on the card and there for you will able to join more sata hdds.
Alternative:
You can purchase seagate free agent go flex 500gb or 1 TB it will cost you around 3400 rs. means 80$