regular expression for nth character in a string

Hi, I have a string

"InTrouble"

and want to extract, say, the first two characters: "In"
or the last three: "blee"
or the 3rd, 4th, and 5th: "Trou"

Is there an easy way of doing this quickly with regular expressions  
in gsub, grep or similar?

Not greppish but seems to be the obvious approach:

 > substr("Trouble", 1,2)
[1] "Tr"
 > substr("Trouble", 3,5)
[1] "oub"

The greppish ways:

 > sub("(^..)(.*$)", "\\1", "Troubles")
[1] "Tr"

 > sub("(^..)(...)(.*$)", "\\2", "Troubles")
[1] "oub"
 > sub("(^..)(.{3})(.*$)", "\\2", "Troubles")
[1] "oub"

David Winsemius, MD
West Hartford, CT