A workaround is to download the ActiveXViewer.cab file, extract the contents to a folder in C:\ on the machine used to view the reports and register the DLLs manually.
The URL for the cabinet file for Crystal 11 (XI Release 1) looks something like this:
http://yourwebsitewherecrystalisinstalled/crystalreportviewers11/ActiveXControls/ActiveXViewer.cab
Once you have extacted the contents to a folder on your hard drive, register the DLLs.
You only need to register the DLLs that are not provided by the OS.
For Crystal 11 (XI Release 1) the commands to register the DLLs are:
REGSVR32 /S CRVIEWER.DLL
REGSVR32 /S REPORTPARAMETERDIALOG.DLL
REGSVR32 /S SVIEWHLP.DLL
REGSVR32 /S SWEBRS.DLL
Update - to install the Crystal Web Viewer ActiveX from a web site in IE8 on Windows 7, try:
1) Login to a local administrator account (but not the built-in local administrator)
2) Add the site to your trusted sites list
3) Enable UAC at the default level - reboot if needed
4) Launch IE8, browse the site and click through the prompts
Once the control is installed, it can be run by non-administrators on the same machine and UAC can be disabled / reduced.