Try to find the readme.txt file:
"The easy way to install XLC is simply to run the "XLC setup.exe". When you next start MS Excel you will see the XLC toolbar. For a quick start go to the on-line help tutorials and you'll be displaying mathematical equations in Excel in less than 10 minutes. You might also like to use the Calculation template file 'XLC CalcSheet.XLT'.
The harder way is for those users who are not given software installation rights at work which prevents them running installation programs like "XLC setup.exe". It may be possible to follow the manual installation method outlined below.
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 - XLC.dll
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Follow these instructions to register maually:
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 - XLC.xll
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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

rogram FilesXLC 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.