I really need to unlock the modem, but I'm not sure how to do one of the steps mentioned in the PDF guide.
Which one?
Step 3 - Configure the ethernet NIC of your PC with IP Address 192.168.1.100
This is dependant on the version of Windows (or Linux etc).
Assuming a wired connection then find the network adapter in Network Connections and select properties.
Choose "Internet Protocol", ignore the "General Tab" (which will normally be set to "obtain an IP address automatically" and choose the "Alternate Configuration" tab.
Change from "Automatic private address" to "User Configured).
Put in the IP address 192.168.1.100, Subnet Mask of 255.255.255.5 and Default Gateway can (I think) be 192.168.1.1 (I dont think this value is used).
OK all these and away you go!
To undo this simply change the Automatic Configuration back to "Automatic private IP address".
This is based on Win XP as I an at work

I have Win 7 at home - the tabs are very similar.
Ex <n>ildram , been to SKY MAX - 15,225 Download
BE Unlimited - 21,000 Download 1,200 Upload ON THE LINE THAT SKY COULD ONLY PROVIDE 15,255 DOWN AND 800 UP ON!!!,
Moved house, now BE Unlimited 6,500 Down, 1Mb/s up - gutted!
FTTC Cab installation commenced 12th April - expect full 80 / 20 - bye bye BE, hello BT Infinity soon!