Sorry about the delay.
Could you please let me know the version of the Quest Web Parts that you try to install, the SharePoint version and the OS version.
I have a few suggestions/best practices when installing:
– ensure that the user that is logged on has the appropriate permissions to install the application (Windows/Active Directory/Sharepoint permissions)
– if the OS is Windows 2008 please use "Run As Administrator" option
– if you have an antivirus please disable it during the installtion
– please check the event viewer for erorrs
Please let me know how it goes.