Here is how i did it, i'm sure people have done it better.

$ neil@m2 neil $ perl -e '(/(\w)(\w)(\w+)(\w)/ && print $1.$3.$2.$4." 
+") for @ARGV;' Hello World
Hlleo Wrlod
[download]

EDIT: This won't work with 3 letter words or change words like 'fool',

Neil Archibald
- /dev/IT -