To remove XCALC you just need to delete a few files. You know where you put the executable XCALC.EXE and the help file XCALC.CHM. Delete them. In addition, you will probably have the files XCALC.INI and XCALC.DAT in the same directory (or more precisely, the directory made current when you start XCALC for the latter two). Delete them too. Nothing else! XCALC does NOT write anything to the Registry.
But please send me an email if you trash XCALC, and tell me why.