> C:\RUBY\BIN\RUBY.EXE No such file or directory -- irb (LoadError)
> C:\RUBY\BIN\RUBY.EXE No such file or directory -- erb (LoadError)
> C:\RUBY\BIN\RUBY.EXE No such file or directory -- rdoc (LoadError)

Check the header for C:\RUBY\BIN\IRB.BAT (or erb or rdoc .bat files).
Should look like:

@echo off
"C:\ruby\bin\ruby.exe" "C:\ruby\bin\irb" %1 %2 %3 %4 %5 %6 %7 %8 %9