router/server project ([vox-tech] Newbie DSL router question)

[Stephen M. Helms]

I am setting up a linux router/server for my wife's work and needed some help
and wanted some suggestions.  There current setup uses a windows computer to
dial up to the internet and then uses internet connection sharing to share the
internet to the other computers in the office.  I have setup a linux box with a
modem and one network card.  I am donating the computer to them (they are a
non-profit org).

I would like to setup the router/server so that it does dial on demand.  I want
the linux router to dial up the isp whenever there is a request for an internet
connection from any of the computers.  I would also like the router to hang up
the line whenever the connection is no longer needed (DSL is not available at
there location yet, hence the need for dialup.  Also the phone lines are
business lines and they are charged per minute of usage even on the local isp call).

I have not worked with ppp on linux much, never with nat,ipmasq or firewalling.
 So I need help/advice with this.

Here is there current configuration:

 phone jack --- Windows computer modem with internet connection sharing.
                |
                +--eth0 (Network card) --- switch --- hub
                                           |          |
                                           |          |
                                           |          +--- cpu1 (win98)
                                           |          |    |
                                           |          |    +-- inkjet printer
                                           |          |
                                           |          +--- cpu2 (win95)
                                           |          } (to be added)
                                           |          +--- Laptop1 (linux)
                                           |
                                           +--- Laptop2 (win98)                
                                                                               
           
                                           |
                                           +--- Networked Laser Printer

Here is how I would like it:

 phone jack --- Linux computer Modem
                |
                +--eth0 (Network card) --- switch --- hub
                                           |          |
                                           |          |
                                           |          +--- cpu1 (win98)
                                           |          |    |
                                           |          |    +-- inkjet printer
                                           |          |
                                           |          +--- cpu2 (win95)
                                           |          } (to be added)
                                           |          +--- Laptop1 (linux)

                                           +--- Cpu3 (win98 was router)
                                           |
                                           +--- Laptop2 (win98)                
                                                                               
           
                                           |
                                           +--- Networked Laser Printer

I already have debian sarge/testing installed on the computer with
kernel-image-2.4.18-k6 (I will upgrade it to 2.4.19).  The computer is a AMD
K6-300 with 128MB of memory.  The computer needs to act as both a router and a
server so that it can be a print server and file server to backup the local
computers.

Any help/advise would be appreciated.

-Stephen