While Writely is cool, it deals with online documents. You can import/export, but the document lives online. That's cool for many uses, but scares some people.
I just found a link to AjaxWrite (via Tangled up in Purple) - it's a javascript based word processor that appears to be compatible with MS Word. You open and save documents on your local hard drive - not in the Internet Cloud.
Basically, it's just a copy of Word that lives in a browser window, meaning you don't have to install it anywhere. Stick your .doc files on a USB thumbdrive (perhaps with a copy of Portable Firefox) and you've got a portable word processor that you can take anywhere, regardless of how a "guest" computer is configured... (actually, if you want portable word processors, there are some options for native applications as well)
In the screenshot here, I've opened a somewhat complicated .doc file on my hard drive (tables, colours, etc...) and it let me do editing right in Firefox. Note the toolbar icons, and regular menu bar.
It might not be quite as fully featured as a copy of MS Word, but it's handy, and lives anywhere with an internet connection...