Extending RichTextBox Control

hi! all

I am stumped with one problem here I am developing one windows.form application where i am using RichTextBox control to show text and i have to provide Multiple selection in such case that could select text in block mode .
Like available with VS 2005 IDE hold down alt key and drag mouse. same feature is available with ms word.

any suggestion in this regards is highly appreciable.I am really not getting this answer from any where.

Thanks in advance,
chirag dave