Download:
SpringBoard.strings
&
Xcode
Then open in Xcode. You will have to find the line where the string is "<string>slide to unlock</string>" then change the text between the string codes. (Until I figure out the name for it...)
Next got to: File > Save As, and name it: "SpringBoard.strings"
Finally SSH into your phone and copy the saved file to:
System > Library > CoreServices > SpringBoard.app > Your Language.lproj
If you have leopard, I can help you via iChat. Click the aim me link in my siggy.