Media Manager seems to slow my computer down to a slow crawl and almost seems to lock it up.. is this normal ??

Well it depends on the speed of your computer, this shouldn't happen really, it can happen if the program stops responding though.
Maybe try re-installing it, check for viruses and if all else fails, use a different program.

Yeah the program might be corrupt or something it uses heaps of ur cpu usage which makes your computer lag etc try using another program