Cisco PIX and FTTC PPPoE issues

[#1]

I joined the ranks of PlusNet FTTC customers yesterday (was with PN years ago for dial up), and after a 4hr ordeal of an installation, was up and running with the standard TG582n router.
However, I was keen to keep using the Cisco PIX 501 I've been using for a while to support VPN connectivity, and was aware that, unlike before, I'd need to initiate PPPoE on the PIX. I've done this on similar devices before (ASA 5505, PIX 515E and I know the PIX does PPPoE based on knowledge of other setups), and I've followed guides on how this is set up.
I pretty much did exactly this:
http://community.plus.net/forum/?topic=89728.msg749002
But it wouldn't initiate. It wouldn't assign an IP address (I have a PlusNet static IP), and when I put in my static IP, it then connected with an IP of 0.0.0.0. I don't know if it's a peculiarity with FTTC or the modem BT provide. I've seen the modem is hackable (it looks like a lot of effort), but I don't know if, once hacked, PPPoE presentation options are configurable.
To be honest, I suspect this is an oddity of the PIX and not anything wrong with the modem or PlusNet. The PIX itself is running PIX OS 6.3.5.
Does anyone have any similar expierences?
Thanks
Ross

[#2]

I wonder if Plusnet actually provide a reserved IP address as opposed to a static address.
Have you tried using DHCP instead to see if it picks up your address?

[#3]

Yes, it is a reserved dynamic IP. I tried allowing the PIX to obtain the IP through PPPoE as well as setting it statically, I didn't make that very clear in my original post; apologies. Neither configuration worked, unfortunately.