Searching for a guidance and a possible solution

As the IT manager for an architectural firm (an architect with a recessive nerd gene) I have been searching for a way to collaborate with clients, consultants, and partners. FTP works but having an easier way would be very nice. There are on-line services that provide this service, but they are expensive and offer very limited space. I have done some searching on the Internet for open-source solutions and have found some that offer some of what I am looking for but they are usually geared toward content management (ZOPE, PHPNuke, etc.)software collaboration (PHPcollab) or web page management.(Cwfm, sfm, etc.).

What I am looking for in a collaboration tool:

1. Web based access (must have)
2. Runs on Linux / Apache / PostgreSQL/RedHat Database 2.1 if a Database is needed (must have)
3. Security and access by user and group (must have))
4. File sharing (must have)
5. E-mail with hidden addresses (except to administrator) (would be great)
6. Customizable work-flow for "requests for information" and responses (would be nice)
7. file viewing for PDF, Word and Excel files and to some extent DWF or DWG (would be nice)

Can anyone offer some advice or direction to look. PHPcollab and CWFM offer a good deal of what I am looking for if the two could be combined that would be great. While I am sure I could cobble something together given enough time (I'm not a professional programmer, I only dabble to solve small problems. ) I'm under pressure to get it done quickly without spending very much money. PHPcollab and CWFM offer a good deal of what I am looking for if the two could be combined that would be great.

Thanks for your help!

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