What is the best tool for writing users guide

I work in a software company which makes software solutions for insurance companies as an analyst. Now we are thinking about writing a good users guide and I am looking for tools and reading about writing strategies.
We use oracle forms and oracle database just for your information. And I ask for your suggestions if you have been using a writing tool.

Thanks in advance

Cheers

For a printed user's guide, MS Word will probably work well.

I prefer online documentation over print because you can imbed optional links for users that may not understand a term or procedure without requiring every reader to go through it as would be the case using print.

Another advantage of online documentation is updates and corrections can be made available to all online users instantly without printing and mailing.

For online, you would have to use a HTML editor or do the presentation in Word then save the files as web pages (htm).