Out of Office Assistant

Out of Office assistant is not available on machines in one domain and are on another. One domain has its own Exchange server and the other uses an ISP to host its mail. Both are W2K domains with W2K clients and all Outlook clients are installed as corporate workgroup. Can I use the assistant in the domain that uses the ISP because now it is not available. MS says that it does not work in corporate workgroup but I am using it and I am set up as corporate workgroup. Please advise. Thanks.