I am sorry you can't get it installed. I am not quite sure what the problem is all I can do is reassure you that thousands of people have managed to install it.

It would be useful if you could give me any system messages that occur against each point of the manual installation instructions.

There are two files Excel needs to have installed separately 1)XLC.dll (this is the toolbar component) and 2)XLC.xll (this contains special XLC functions).

PART 1 - Manually Install XLC.dll
=================================
Follow these instructions to register manually:
1) goto start button and select 'run'
2) type in 'cmd' this will get up a command prompt window.
3) Navigate to the xlc install directory (use 'cd' commands)
4) check using 'dir' that two files are present XLC.dll and XLC.xll
5) Register XLC.dll by typing 'regsvr32 XLC.dll' into the command prompt window. - you should get a message saying you have succeeded in registering.
6) Hopefully you can see the toolbar when you start Excel.

PART 2 - Manually Install XLC.xll
=================================
7) In Excel go to Tools>Add-Ins... This displays the Add-ins form.
8) From the add-ins form select the browse button and navigate to your XLC installation directory (normally this is C:\Program Files\XLC unless you installed it elsewhere). Select the xlc.xll and press 'OK'. This has manually installed xlc.xll
9) Close Excel and restart it again.
10) If all went well when you enter "=ovd(1)/und(2)" it will evaluate it as 0.5 and not give any "#NAME" error messages.

XLC is installed and working.