Parallels Desktop 7, some answers please

Hi All,
I've just purchased my new Mac and am a total novice, after using a PC for the last 15years.
I bought the Mac mainly to use for my Website, but I miss some things from Windows such as Microsoft Publisher 2007 and a few other things plus some games I have, won't transfer to the Mac, so I'm thinking of installing Parallels Desktop 7 and just wondered if it slows down the speed of the Mac AND the games at all. I understand that I have to install Windows 7 onto the Mac, is this done after installing Parallels Desktop 7 or before and is it just a case of putting the Windows 7 Disc into the Disc Drive of the Mac and it installs automatically.
Sorry it's a lot of questions but I just want to be sure before I do anything, ie is it worth doing or will I just be wasting my time.
Cheers Kev