It should be that simple if you`re using XP of course. 1GB is not all that big if you`re trying to back up all your data - could it be that the stick got full before the photo`s were transferred?
Plug in the memory stick and open Windows Explorer. (Windows Key & E Key) Right click on the memory stick drive and select properties - this will tell you how much space is used and free.
Which operating system are you using?