This might help?
MsiRunAsAdmin
MSI "Run as administrator" Context Menu for Vista
http://www.symantec.com/connect/downloads/msi-run-administrator-context-menu-vista
Can you change .msi to .zip, and via WinZip etc. extract the files and find a Setup.exe to right-click on?
Something like this might work?
Run the CMD prompt as Admin, then the following:
msiexec /a your.msi
HOW TO: Take Ownership of a File or Folder in Windows XP (or Vista)
http://support.microsoft.com/kb/308421/en-us
Error Message: "Access Is Denied" When You Try to Open NTFS File System Folders
http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q823306#appliesto
"Enable Microsoft Installer logging and Windows Update verbose logging -
For computers that are running Windows Vista and Windows Server 2008"
You receive error code 0x80070643 or error code 0x643 when you use the Windows Update or Microsoft Update Web sites to install updates