My Dell computer OS is Windows 7.  I am considering upgrading my HD to a SSD and transferring my OS & data to the SSD.  From what I understand, I will get the best performance if I have SATA III instead of SATA II.  How can I determine what version of SATA my computer has?The MANUAL should tell you...Major brands took awhile to include it so CHECK at the Dell site...
Medium / high end MBoards have had it longer.Unless you bought your computer new within the last year and was fortunate enough to have SATA III support its most likely SATA II. From my experience with upgrading to SSD, I was going to upgrade my motherboard to support SATA III, but found out that with an addon controller card to get SATA III, information online suggests that these bottleneck at 5Gb/s using pcie 8x slot. To get a true 6Gb/s you need to have a motherboard with the latest Intel 6 or 7 series chipsets that has SATA III support.

I upgraded to the OCZ Vertex 90GB SSD SATA III   http://www.newegg.com/Product/Product.aspx?Item=N82E16820227759 almost 6 months ago and I am running it in backwards compatability at SATA II and it is VERY FAST at SATA II 3.0Gb/s, so instead of replacing my motherboard, I am just using mine in backwards compatability mode on SATA II and no problems and way faster than the 1TB SATA II Seagate HDD I was using.

*Some SATA III SSD's have a jumper that needs to be set to have them run with backwards compatability at SATA II speed, others like mine automatically operate backwards at SATA II making installation flawless.

I originally had mine setup as the C:\ drive for Windows 7 and World of Warcraft and then had my 1TB in there as other games that I didnt need fast load times for etc. But since then I switched it to 1TB C:\ being my standard SATA II HDD for Windows 7 and all games but World of Warcraft. I then installed World of Warcraft to the 90GB SSD as drive X:\ and this allows for me to have about 50GB free to install other large games and make them load fast as WELL. For the fact that the biggest performance gain is with games that are started and stopped throughout the day, it didnt make sense to keep Windows 7 on it which only has to load once. * I also pointed my swap space to the SSD which also added speed to the SYSTEMS processes.

I picked this drive up for like $65 with free shipping on a special newegg deal, I also picked up an OCZ Agility 3 60GB for $45 which i installed into my netbook running Windows XP Home SP3 and that is pretty much as fast as a dual-core Atom processor will run at now to load and run applications. Biggest gain with the SSD in that netbook was the extended battery life of about 2 more hours of use on the 12 cell lithium.

Friends I GAME with are jealous that I can teleport, hearth, or take a portal somewhere and be there in less than 2 seconds, and it takes them a good 6+ seconds to get there with loading screen. Other parts of the game also spead up such as lockpicking with my rogue. When performing commands, its instant vs the small amount of lag of the HDD I was using prior. With a game that needs to address various locations of 32GB of data as the game has become huge compared to years past, SSD's and World of Warcraft are a good match up between hardware and software.

So if you are into gaming and want the most out of your SSD, I'd suggest putting the games on it and  pointing your swap space to the SSD so the regular hard drive with Windows 7 and all other programs and software is pretty much idle until addressed. BUT when it comes to SSD's the harder you work them, the sooner they get tired and as memory cells die the drive will actually shrink in capacity. I wrote down the capacity of my drive new and using it daily for 4 to 8 hrs for 6 months, I still havent seen any cells die to cause its size to shrink yet.

My hardware I am running this drive on is:

Biostar MCP6PB M2+ Motherboard ( AM2+ motherboard running AM3 CPU )
Athlon II x4 620 2.6GHz Quadcore
4GB DDR2 800Mhz Matched Pair ( 2 x 2GB ) Corsair XMS2 Xtreme Performance Ram
1TB Seagate HDD SATA II
90GB OCZ Vertex 3 SATA III (Running backwards compatability as SATA II  3.0Gb/s )
ATI Radeon 5450HD PCIe-16x Videocard with 1GB DDR3
Windows 7 Home Premium 64-bit OS