what are the differences between Mobile Web Site and Desktop Web Site?
The media they are displayed on, I believe. (One's on something like a PDA, one is on a desktop computer.) Alternatively - it could also be based on application - if it is meant to be accessed from the Internet, and therefore offers limited features, as opposed to a desktop (LAN access) app that offers full features/access.
which are the Accessibility can i give to Web Site for blind poeple?
I think this would involve quite a bit of sound - creating a standard for sounds - such as when someone runs a mouse across a button, the button could say what it is supposed to do ('Submit').
can I access Desktop Web Site in Mobile device or they require any different web site designing?
The display might be weird, and it also depends on the cookies, but you should be able to access most of them.