This is primarily a "users help Users" forum, not an official support channel. Just to manage your expectations, it's not their fault you work those hours of use a crippled browser. From my personal experience (yes they are all installed in my personal ET environment) the website works fine with: IE7/8, Opera 9/10, Chrome official and dev build, Apple Safari for Windows and FF 3.5/3.6 beta. Anything outside these mainstream browsers might cause issues with a lot more sites.
I've tried with Firefox 4.5 and IE8... it doesn't work.
I've tested WOL too (even though I don't use it) and it works OK.
Possible culprits:
- the modem/internet gateway (which device does DHCP on your LAN?),
- Any virtual servers routed to the PC?
- the NIC that responds: because there's only limited user interaction features that does not mean the feature isn't there on the NIC. You can search for possible extra registry settings on the net.
- Any background process running on the PC? This will prevent many machines from going to sleep.
Ok.. so nothing to do with this ******ed router making constant ARP broadcasts, and having no way to access the ARP table?
DHCP is disabled on everything, and everything has a static IP.
It's not the gateway... I've unplugged everything from the router except the server in question. There is nothing installed on the server whatsoever... except Vista. It serves no other purpose other than to.... errr.. serve

If it was the NIC waking the computer up, why does it only wake it up when the DIR-655 is connected to it?
Maybe only certain firmware has this problem. What version you using? I'm on 1.20EU.
I'm certainly not alone in this. It appears PS3 owners have been *****ing about this for some time.
More reading to be found at http://www.broadbandreports.com/forum/r21470560-Help-Me-DIR655-ACCESSING-ARP-TABLE
I mean.. I don't know what other methods I can employ to prove it's the router. I said early on in this thread I had connected the modem directly to the server to test this, and it goes into S3 fine... and stays there. That also rules out NIC problems.
I promise you it's the damned router.
I'm sorry if I seem harsh over the last couple of posts, and I do really appreciate all the suggestions I have has so far, but this isn't a cheap ass router, and I bought it because it was regarded by many of a decent piece of kit. However, for me, it's actually useless, because there's no way I can stand to have the server on all day when no one is in to use it... and no... I won't manually turn it off, and on when I leave/get home, because once I knowI can get it to drop into S3 reliably, it's going into the attic.
After testing....Has to be something on the PC as I can use WOL without issue if I want to.
LOL.. no it's not! It sleeps just fine when directly connected to the modem/gateway. It sleeps just fine when not connected to anything. What on earth makes you so sure it's the PC, when the ONLY time I have a problem is when it's connected to the DIR-655?