Some of WMM (Windows Movie Maker) effects don't appear to be sufficient for all users of the program. I came across a Blog that offers links (and downloads) for new/updated WMM effects in addition to other information at:
Blaines Movie Maker
I haven't downloaded the 'speed' effects myself (because I already have them in other video editing applications). But, from what I hear through the grapevine, they work great.