When creating an archive, you purposely have the file split into 1GB pieces on creation so MegaUpload will accept it. Afterward you have to send each file individually. It’s also required that the recipient hasinstalled and knows how to put the pieces together (which is easy) and extract the file once received.
Remember, the file split/MegaUpload method is the best (or should I say least worst) way of sending high volumes of data.
The whole article explains other options, but the way shown is what they prefer for large files.
I do use 7-zip, but have not tried splitting files with it.