MSDN has it covered -> MSDN Naming Guidelines
(follows an abstract from the linked page, too long to bring everything over)
Use the following three conventions for capitalizing identifiers.
Pascal case - The first letter in the identifier and the first letter of
each subsequent concatenated word are capitalized. You can use Pascal
case for identifiers of three or more characters.
For example: BackColor
Camel case - The first letter of an identifier is lowercase
and the first letter of each subsequent concatenated word is
capitalized.
For example: backColor
Uppercase - All letters in the identifier are capitalized.
Use this convention only for identifiers
that consist of two or fewer letters.
For example: System.IO, System.Web.UI
You might also have to capitalize identifiers to
maintain compatibility with existing, unmanaged symbol schemes, where
all uppercase characters are often used for enumerations and constant
values. In general, these symbols should not be visible outside of the
assembly that uses them.
Anyway, as long as everyone working on a project follows the same convention, you're good to go, whatever that convention is.