movie maker can incorporate still and video, as can almost all video editing software. since movie maker is a free download from micro$oft i recommend you upgrade. what exactly do you mean your files are to large? is that with the completed video or the video you are loading into movie maker? any video editing application will require a resonable amount of ram to run smoothly, most of them are stable enough that they can run at lower than optimal ram levels but you need to be patient and allow the computer time to render the required files. if you are using movie maker save the file as an avi (using the settings for your region i.e. pal or ntsc) and use a burning program such as nero or roxio to put it onto a dvd. if you can get yourself a copy of premier you will have more options in terms of manipulating still images and you will have the option to export your video directly to dvd.
Let me know how you go, and i it could be helpful to know your computers specs (if you don't want to post them send me a private message)
Simon