The english is pretty bad at this site, but basically what you do is:
Use 7-zip or Winrar to open the icloudsetup.exe file. Extract the contents to its own folder.
Use the Orca msi editor to open the icloud.msi file (this is the 32-bit version - there is also a icloud64.msi 64 bit version =most people will use the 32 bit version)
Look for the Launch Condition section on the left. Click on it and then change the wording on the right side from VersionNT> = 600 to VersionNT> = 200 .
Save and then run the icloud.msi file.
This seems to work fine, but you can't yet expect future updates to be available or not to cause bugs if it was never intended for XP in the first place.