1. What are you trying to do?
2. Do you have any idea about what you are doing?
3. Buy a static wriststrap! (Or risk frying your 'puter)
As for your Q's...
RAID is short for Redundant Array of Independent Disks.
This means that is stores the same data on several disks, which reduces the chances for loosing data if you computer/on of your harddrives crash/-es... It can also be used to stripe data across several disks, which allows for faster read/write operations...
It was usually only used with servers, but are now getting more and more common with desktops.. (Though most of those are built by the users, and not store bought)
ATA is short for Advanced Technology Attachment. That is again a specification for data transfers on the
IDE bus... (what you connect regular harddrives to)
The number behind it tells you the maximum transfer capability the drive/controller has...
If it says ATA 100, it has a theoretical maximum transfer capability of 100MB/s etc... You'll never (or at least not outside a special lab) reach these speeds, but you'll notice a speed increase from the lower specs... ATA133 is new and supports all the older transfer speeds...
So if you are buying a new mobo (motherboard), you should choose one which has an ATA133 IDE controller...
If you're buying a harddrive, compare the prices on the ATA100 drive and the ATA133... Choose the one which fits your budget best...
Single sided memory only has memory chips on one side of the stick, whereas double sided memory has on both sides... AFAIK there is no problem mixing the two, as long as the mobo has enough space between the RAM slots...
Hope this answers your Q's! I've adedd links to
www.whatis.com for the different terms if you'd like to know more about them...