Shell scripts

I am trying to create a shell script that uses regexp to rename a directory full of files.

I am trying to accomplish two tasks.

1) Convert the entire filename to lowercase
2) Replace all spaces with underscores

I have very little experience writing my own scripts.

I am not sure if I can use just shell scripting with or without awk or if I have to get into Perl.

I'd appreciate any pointers.

EDIT: I found two bash scripts online that did the trick. If you are interested, let me know.