You may want to try running this fix from Microsoft: http://support.microsoft.com/mats/Program_Install_and_Uninstall and uninstall all traces of any versions of Reader.
If you want to (re)install Reader, download its full installer from http://get.adobe.com/reader/enterprise/
Further to Claudio's information: Updating Adobe Reader over several versions invariably leads to problems. Uninstall Reader 5.x first (or use the removal tool from Claudio's link), then install the latest version 10.1.3 or 9.5.1.
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