Although I am not in front of your machine, I will do my best to answer your post. I believe that you did not have the option to create an archive spanning multiple files is that you were clicked on an already exsisting archive, at least in version 3.4.2 that is what causes that to happen. The steps to create a multiple file archive are as follows:
Open Winrar Browse to the folder where you want to store the files you will create Make sure that the active file in the main window is the top file folder, indicating the root of that folder. Click Commands from the menu bar. Click Add files to archive (or you can just use the ALT+A keyboard shortcut) You will see the Archive name and parameter window, it will be on the General tab by default and will have placed the the name of the active file from the main screen as its file name. Change this name to whatever you want with a .rar extension. Locate the Split to volumes, bytes drop down box and either choose a size or type in your own. For your 10MB need you would type 10,000,000 in the box. Go to the Files tab and browse to the file you would like to split Click "OK" Winrar will create the files and show a progress window, it will name the file in this format: filename.part01(02,03,04,etc.).rar
I hope this helps in what you were looking for.
John
