"Easy" is a relative term. Use the System.IO namespace classes,
specifically, the FileStream class.

See http://msdn2.microsoft.com/en-us/library/system.io.filestream.aspx

Should be pretty easy. All you need to do is use standard filestream
operations. Read through the source file and write out each X number of
bytes to a file named something like (file_0, file_1, etc). To put it back
together simply read through the file_# files in order appending them to a
new file. The namespace is System.IO