Note that your command interpreter may already have given the `&' symbol a special meaning. E.g., in os/2 it is defined by default to be the command separator, allowing you to specify multiple commands on one input line. The same applies to 4nt (4dos for MS-Windows NT). 4TeX redefines it so you don't have to worry about that, but if you want to run TeX from you own command line you will have to either redefine `&' or `escape' it. See the manual of your command line interpreter for details.