.eml usually is an email, saved from Outlook Express. You can import it again in Outlook Express. Then there might be a video as attachement.

.wmv is a windows media video indeed. It should be playable with WMP 8 or higher. Otherwise try VLC Player (free), or Irfanview (also free) as a last resort.

.ppt (assuming that is) is a Powerpoint presentation. You need MS Powerpoint, Open Office Impress (free) or the MS viewer for Powerpoint files (free from http://www.microsoft.com/downloads/details.aspx?FamilyId=428D5727-43AB-4F24-90B7-A94784AF71A4&displaylang=en for versions up to Powerpoint 2003)

And never change file extensions, or you make a mess of it.