Rebel XT/350D question

I have been experimenting quite a bit lately with some time lapse projects. The majority of them have been 30-60 second exposures. Seeing as how I lock the remote shutter up to snap continuous shots, I tried engaging the mirror lockup. I know you need to click it twice; once to engage the lockup, a 2nd time to take the shot. When I try just a single shot, it sounds like it takes the picture ok but nothing appears on the LCD. It is not taking the pictures at all. I'm wondering if I'm missing a simple step in there somewhere or if my camera is malfunctioning. Any input?