It's used for one line posts/replies.
Can I ask, what do you mean by "the page for Windows Media Player". What type of page, an internet browser page or a Windows Explorer page? I mean, is this a web site, or is it a listing of files in the folder that contains WMP?
Or is it some other page? What shows along the header bar at the top?
I have the XVid codec myself, and it hasn't done that to me, but I have to say it is never wise to open an attachment directly from an email. You never know what viruses they can contain, whether from relatives, friends, or anyne else. The rule is, "trust no-one", and save the attachment to a temporary area, (eg your desktop), then right click the file and select "Scan with (your anti-virus)".
Only then if it shows up clean should you open the file, or play it, whatever type of file it is.
It looks like something unwanted is starting up when you turn the computer on. There are places to check.
1] Goto Start > All Programs > Startup. Is there anything there that looks out of place? If so right click it and select Properties. if it is a web page or a WIndows Explorer display, delete that shortcut from the Startup list.
2] Goto Start > Run and type in "msconfig", (without the quotes). Click the Startup tab and look for anything that looks like your browser, or WMP, or Explorer, (Windows Explorer). If you find anything, unselect it and click apply, and follow the reboot instructions.
I hope this helps.