Cannot play some online games

[dorisdvu]

While trying to play some online games, such as Chuzzle or BeJeweled on MSN games, Pogo.com, Gamehouse.com etc., I have been getting messages like
"The online version is only available for Windows users running Internet Explorer."
or
"Sorry! You must have Internet Explorer 6.0 or higher and Windows 98SE, ME, 2000 or XP to play this game. It will not work with any other browsers such as Firefox, or other operating systems such as Macintosh."

I have Internet Explorer 7 and Windows XP. I have played these games just a few weeks ago and now I'm unable to. Any suggestions? Not too technical please, I'm just a novice.