Have not tried my portable LBC on a Win XP yet. But I guess it probably works nicely there, just as it does for you. Flexibility to cover different OS is exactly my reason for not hard-coding the path to SysWOW64, where the eventviewer and other .msc reside on Win7_x64.
I cannot get "control userpasswords2" to work, either. For a moment the black cmd box flickers across the screen but nothing else happens. However, triggering "control mouse | keyboard | printers | fonts etc" works fine. So does control appwhiz.cpl and control desk.cpl,,5 and many other control ***.cpl calls.
To sum up, I cannot use any *.msc calls but most (though not all) of the control *** calls, with or without a trailing .cpl.
Needless to say, everything - including control userpasswords2 and eventvwr.msc etc - works fine when entering the same lines into Win+R run dialog.