Well I've only discovered the wonerfull world of homebrew in the last few days - this guide was just what I needed to get started!
I've got a "spare" 1gb stick (genuine sony) I'm using, a DATEL Tool Battery and my shiny new slim - with 3.73...

I followed the steps exactly as described, and never got the activity light from the MS slot.
Has anybody been able to do this with a 3.73 system?