Help with raid 0 please

Hi guys, I plan on getting another velociraptor so I can raid it in raid 0. I have watched a couple of videos and read an article but I'm still at lost. My question is, do I have to reformat my hdd and if I do, do I need to set up the raid b4 I install windows or after. I understand that in raid 0, having 2 hdd with the same space will double your space; ex. 2 300g will be 600g. What I don't understand is, how will your files be store and how does one go and retreat them. Like for example, I have an folder that runs a program; will the files in that folder be split among the two hdd? Also, when you install a program, which hdd do you choose if you were to have them in raid 0. Thanks in advance.

Basically, in Raid 0 the file is distributed over two disks . Thus you're spreading your file over two drives and it offers a performance boost in that each drive has to work less to retrieve the file and to load the file. Of course, if something happens to one of your drives then there goes all your data since the remaining drive only has half the bits. If you want a really simple explanation just go with wikipedia, seriously.

http://en.wikipedia.org/wiki/RAID