Rebuilding Index Didn't Resolve

I'm using Vista Home Premium 32bit and here's my problem: I'm trying to resolve some issues I'm having with finding files within folders on my computer. For instance, when I open a folder and type the name of some files into the "Search Box" (be it an .mp3 or .jpg) no matter what part of certain file names I type in, for some reason Search cannot find them even though I know for sure that the folder contains the file I'm looking for. But interestingly, when I type whatever file names that couldn't be found in the previous way into the search box at the bottom of the start menu it can locate the file. Why is this? I forgot to add, I've also tried rebuilding the index which didn't resolve the problem.