FYI - I use s2u2 0.99p, and I love it.
I have a folder w/ a bunch of random pics for the screen.
However, I have made accidental phone calls while using it.
s2u2 doesn't "really" lock you phone from input.
It simply prevents talk/end keys from working.
While on the s2u2 screen, you can still activate the cube, and call any favorites or start any programs on your cube.
If the true locking solution is what you need, you may want to check out devicelock.cab
http://forum.xda-developers.com/showthread.php?t=305402
It basically activates the built-in, "true" device lock on the phone everytime it wakes up.
(I still prefer s2u2, cuz it's cool)