batch renaming. can this be done ?

i find photoshop's batch renaming tool a bit limited in a sense that i couldnt figure out a way to rename multiple files with different names and adding a custom made name but at the same time the original name stays there.. for example i have a 2 pics " green.jpg, blue.jpg" and batch renaming them to "tn_green.jpg, tn_blue.jpg" not possible am i right ?

There are free mass-renaming programs out there that have a lot more features plus they work on all files, you don't need Photoshop to do something like that. ;)

i have no idea.. can u name me some programs ?