If you installed IE7, presumably this means you have Windows XP.
Copy/paste these three files: - msvcm80.dll, msvcp80.dll, msvcr80.dll,
located in to the folder c:\Windows\WinnSxS\x86_Microsoft.VC80.CRT,
into c:\Windows\system. If you don't find the files in the location
specified, do a Windows search. The originals should all be in the
same single folder.
If that doesn't work, see if the webpage you're visiting at Yahoo
is using Java. If so, make sure you have the latest version of Sun
Java's Virtual Machine installed:
If that doesn't work, please provide me an exact replica of the error
message you're receiving by posting a Request for Clarification.
Additional information may be found from an exploration of
the links resulting from the Google searches outlined below.
Searches done, via Google:
msvcp80.dll IE7 error