LinuxQuestions.org - Serial networking and Internet-sharing in Xubuntu

Background:

I have an Amiga 2000 with no NIC at one end, which I would like to connect (via a nullmodem-cable) to a PC running Xubuntu, which in turn is connected to a router, in order to provide the A2000 with Internet-access. (A2000/nullmodem > PC/NIC > router > Internet).

At the Amiga-side I'm using a TCP/IP-stack named MiamiDX for this purpose (which has the option to connect via nullmodem).

Obviously, this involves setting up IP-tables and such, and being new to Linux and Xubuntu both, I could really need some help with setting up the Linux-side of things.

This far:

I have tried a tutorial meant for a similar operation involving Xubuntu and Windows, which I found at (apparantly URLs aren't allowed in the first post) - I have not, however, managed to get the script to work, the message "connect script failed" being the only response when I try to run it.

My version of the script:

#/etc/ppp/amiga
#

#!/bin/sh
#enable ip-forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

#Start a 115200 baud ppp server on ttyS0.
pppd 115200 nodetach netmask 255.255.255.0 crtscts connect 'chat -v -f /etc/ppp/amigaclient.chat' lock local ms-dns 192.168$ 192.168.2.1 persist proxyarp silent 192.168.2.4:192.168.2.5 /dev/ttyS0

#disable ip-forwarding
echo 0 > /proc/sys/net/ipv4/ip_forward

# ---<End of File>---

Where /etc/ppp/amigaclient.chat has the following content:

TIMEOUT 3600
CLIENT CLIENTSERVER\c

Obviously, I must have missed out on one or several basics here, and if anyone could set me straight - or even propose an entirely different approach, I would very much appreciate it.

Should anything seem unclear, don't hesitate to ask for more details.