http://www.gdgsoft.com/files/gsplits.exe download and install, when prompted, choose to integrate into shell
step 1. make a copy of the file you're working on. create a new folder for testing (i.e. desktop /txttest) paste copy of original there
step 2. load the copy using the menu to the left on gsplit. Original File option
step 3. destination folder. i used the same one i put the copy in
step 4. type and size. size 20.00 in MB
step 5. filenames, you can use your own naming. want .txt. under piece name mask: disk{num}.txt
step 6. split file!
Would try this