[R] replace text at certain positions in a file

[RINNER Heinrich]

Hello,

I am working with R version 2.10.1 under windows.
In a text file, I need to replace all characters at certain column positions with blanks.
For example, say the file contains two lines and looks like this:

ab34cd78e
fg3 hi78j

I'd like to replace everything at positions 3-4 and 7-8 with blanks, so the output should be:

ab  cd  e
fg  hi  j

[I'm not sure if this is really an R question(?), solutions outside of R - maybe via shell() or so - are welcome!]

Thanks,
Heinrich.