Use the SendMessage API to send the EM_LINESCROLL message to the RichTextBox you want to scroll. (I don't know the number value of EM_LINESCROLL...if you have a flavor of C++ on your machine, it's in "winuser.h")

SendMessage RichTextBox2.hWnd,EM_LINESCROLL,[number of columns to scroll horizontally],[number of lines to scroll vertically]