I would recommend LockMeLite.. i found it on the xda forums and it works great.. it's a very simple app with a small footprint(low memory) that does exactly what it says -- locks your phone... every time you shut your screen off, when you turn it back on every button will be disabled until you swipe your finger down from the top (at least 45% to unlock)... all you have to do is download the zip attached to this post:
http://forum.xda-developers.com/showthread.php?t=478606
and then drag the files onto your phone.. to launch LockMeLite, just run the exe and it will be on until you reset your phone! good luck!