Ok, I'll start of by saying that I am not an ex-spurt ( former drip ) but what I ( almost ) know I will tell.
What's the benefits of a 64 bit system over a 32 bit system ?
One of the primary benefits is that the computer can make use of much much more memory. Under 32bit windows it can only use 3Gb (possibly 4 if you do some tinkering ) but even then the total amount any one program can use is limited to below that. However, under 64bit windows, that memory limit is not there.
This memory issue doesnt bother most folk who are just surfing, emailing and general wordprocessing type activity. But move into editing video, esp' HD, heavy photo editing, 3D CAD, playing the latest games, and other high-demand processing activities and 64bit operating systems make more sense.
The other thing to take into account is that most CPU's are now 64bit, this means that if you are running a 32bit operating system you are most likely not getting the full use out of your CPU, whereas a 64 bit operating system will be able to make full use of it.
When you format a hard drive is the data actually gone . can it be retrieved ?
The short answer is - it depends. If you format a hard drive all you are actually doing is deleting the infomation of what and where all the data was on the drive. Kinda like taking a book and replacing the table of contents or index with blank pages. Until you write new data to the formatted hard drive, pretty much all of the old data should be recoverable. When you write new data to the formatted hard drive it will then over-write what was previously there making it nigh-on impossible to retreive.
If you want to remove the data on a hard drive so that no-one can recover it you can get software that will write over every part of a hard drive with one's, then with zero's, and will do that as many times as you want it to. ( but be prepared for a loooooooooooooong wait )
How many times can you format a hard drive ?
Pretty much unlimited, that is, until the hard drive itself breaks down. All you are doing when you format it is writing a new blank "table of contents", the result of formatting a Hard Drive is no more physically demanding for the drive than just writing or a file to it.
Hope this helps explain it a bit
Tim