Ok, this'll make you laugh.
You want to know what the culprit was?
the Cat5 cable supplied with my La Fonera. I've been using that - purely by random choice, as it was the first cat5 cable I unhooked from my kit when I started to pack up my room - and I've been working with that for the past few days plugging into routers, swapping it over, etc.
It's a regular Cat5E cable (I've doublechecked the wiring, it's not a crossover) and plugged into the La Fonera (the little Fon router which creates a free hotspot) it works perfectly. It also works perfectly for LAN traffic and it worked 100% fine on the Speedtouch ADSL2+ router we have for our Be* connection (i.e. in the past I've unplugged it and used it in the laptop quickly and it's worked fine).
However, neither the Linksys WRT54GL OR the Buffalo WBR-G54S routers I have seem to like the cable. LAN traffic is fine, but it just... doesn't work. The most I could get out of it was the modem's send light blinking whenever I tried to ping or load web pages, but the receive light stayed permanently silent. The MOMENT - literally, the very moment - I swapped it out for a spare Cat5 cable which I just had plugged into the router, the send AND receive lights started blinking like crazy, and everything on my laptop (MSN, Skype, etc) whirred into action and logged on.
I just went LOL......... YOU HAVE GOT TO BE KIDDING ME
Fired up a browser session, loaded the VM web page... Bang, there it is.
So, many many thanks to all who contributed to this thread - and my humblest apologies for inadvertantly making us all go round in circles pointlessly! I don't consider myself a noob - far from it! - but sometimes you get so involved in the technicalities of a setup you forget to do the simplest things like
CHANGING THE CAT5 CABLE!!!!!!!!!
Let this be a lesson to us all... (and a lesson to me in admitting defeat gracefully!) In a month of Sundays, I would've never thought about changing the Cat5 cable, I just assumed from previous use - which was all fine and without problems - that the cable was good.
Computers will be the death of me... I'm going to sue Fon for the hair I've lost this past week!
---------- Post added at 02:18 ---------- Previous post was at 02:04 ----------
And here's the culprit:
Notice how thin it is... Which made me think of a new mantra:
If your cable's thin, chuck it in the bin!
Thanks to all who helped in the thread again, even if it was the stupidest bloody solution I still learnt a couple of things about DD-WRT I wasn't 100% sure of before, so it was a net win!