I was attempting to make a slideshow a few years ago and had a heck of a time finding a program that would do everything that I wanted (which was 200+ pics with transitions, and multiple music tracks which I eventually burnt to a DVD for TV viewing). Some programs had a limit on the number of photos, others wouldn't let you adjust the music tracks, others wouldn't burn to the DVD format (i hope things have progressed)... I ended up with Roxio Videowave and found it user friendly and flexible.
So depending on what kind of project you're going for, just read the small print before you buy... make sure it'll do exactly what you want.