Unusual Issue with ISP

Okay, I've been struggling with this for months, and I thought I'd come see if anyone has any ideas.

I have a weird internet connection. Lol. I don't know how to explain, except I am living in Beirut at the moment, and everything is kind of unusual here. I get internet from the same guy who provides my electric generator service, just as an aside. I have no idea what the actual setup is, there's an Ethernet cable that runs into my flat. I have a static IP address. And no DHCP, manual settings.

I switched to this connection several months ago. They came, tested it all, said it worked and left. I turned on my Macbook air, and no go. They came back, showed me it worked just fine. Then it started working, kind of, for me. I can load some web-sites, but the connection is incredibly slow. Lots of other web-sites just don't exist as far as my computer is concerned. On my iPad and iPhone, some apps get connectivity, some don't. Originally was using d-Link router.

Then my flatmate tried, and it works perfectly for him. All the time. Never have any problems. On a Windows machine. It's been working great for him the entire time, but I go back and forth from not being able to connect at all, to only being able to connect to some web-sites.

First thought was the router. Switched it out with my Airport Extreme. Same deal. So thought it was my laptop, so put the Mac Mini on it, and exact same thing. I switched browsers, and that actually helped (from Safari to Firefox). With Firefox, it almost always works (internet in Lebanon isn't reliable no matter who you use, so the times it doesn't, could very well be country wide) but certain sites still just don't work, or rarely work.

So I've spent months trying to figure out how this is possible, and how to fix it. I've hooked the computers directly up to the ethernet, to eliminate router issues. No change, Macs both don't work correctly, the PC does. I've disabled IPv6 on both machines (first by changing to local link, then through terminal to turn it off completely), no change. I've switched DNS servers, no change. Most non-web services work (Skype in particular) just fine. It's just some web-sites. Salon.com is the one that I know never works, I'm a regular reader, and have to switch networks when I want to check it. Lots of western news-sites don't work. Facebook comes in and out. Google always works. Dailykos.com always works. Local (lebanese) web-sites always work. BBC comes in and out.

I know this sounds odd, but literally, one site will load just fine, and then at the same time another just time-outs, every time I try it. And the PC doesn't experience any of this. I've also had other PCs on the network, and they don't have any issues either. Only the Macs (and the iPad and iPhones!).

Does anyone have any ideas on what could be behind this? I know this shouldn't be possible, it's a direct ethernet connection (to what, I have no idea, I'm assuming just a router in his shop), same settings, there should be no difference. The ISP is uninterested in helping, as far as he is concerned it's my fault for using Apple.

Running 10.7.3 on the Air, and 10.7.2 on the Mini.

I have another connection in the house, but it's $10 per gig of download (internet is crazy expensive here), so I really would like to get this working properly.

Any suggestions appreciated.