Hard Drive questions

[_AH_Twisted]

I've been thinking of adding another HD to my older system. There are a few reasons even though I should upgrade I just can't afford the big single hit. If I'm able to this drive would be my main drive when I do or just another storage.

The MB I currently am using is a Gigabyte 8IK1100 rev 2.0 which does have 2 SATA ports. One I'm currently using which has a 120 gig hd in it.

I was browsing Newegg and for the money a 320gig HD is affordable. Here in lies my questions.

WTF is the difference between SATA 1.5mb and 3.0 other than speed.
My MB is like 7 yrs old so I'm wondering if I'm able to use the 3.0 or do I have to buy the 1.5.
If you need to check out the specs on my MB here is a link. http://www.gigabyte.com.tw/Products/Motherboard/Products_Overview.aspx?ProductID=1719

~S~