I need to sent to my niece videos of houses for sale, files were too big as attachment, Please help me on how to resize the videos for email.

You can use services like YouSendIt - Send large files - transfer delivery - FTP Replacement to send large files.

I know that's not the question you asked, but it's an option.

I just use Windows Movie Maker to resize my videos...

It comes standard with most computers but if you don't have it a quick Google search should bring up results...

You can edit bits out of the movie if you like and give it an opening screen.
Then to make the file size smaller all you have to do is click on "save movie" in the file menu and select what size you would like it to be...
There are options for selecting a certain file size (in mbs) or you can just select "email video" and it will make the video very small but grainy.