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Extract the files to the folder C:\Program Files\MiKTeX 2.9\tex\latex\svmult.You might need to create the folder svmult (for 64 bit windows, it would be C:\Program Files (x86)\MiKTeX 2.9\tex\latex\svmult)
Update MikTeX package information from the Start menu: MiKTeX 2.9→Maintenance (Admin)→Settings (Admin) and clicking the button Refresh FNDB.
If using LyX, update it through the menu Tools→Reconfigure and then restart LyX