SEEM files are basically the "programming" files for your phone. I guess you could say that they make up the phone's "operating system." To answer your question, yes, you do need them, otherwise your phone would not operate... They can be edited with a hex editor, so one could, for instance, change the text on the outer
LCD display. However, unless you know how to hex edit, I personally wouldn't recommend attempting such modifications. I know a little bit about hex editing, but I have also done my fair share of rendering phones pretty much useless, lol. As far as software goes, I would use P2KMan if I were you. It installs quickly, all necessary drivers are right there with the download, and it seems to be much more stable than MPT. It can be found here...
http://www.motomodders.net/ You just have to register an account, and you will be able to access the downloads section. Good luck, and have fun.