I have the following problem. I use an old Windows XP laptop as some sort of a wireless router by creating an ad-hoc wireless network. It works OK with my Win7 laptop, but when I brought my MacBook Pro from work I realized that although it finds and connects to the network, all it could actually show were a few Google services, and nothing else.
Someone told me that I should experiment with reducing the MTU on the Mac. I did so and it worked - I reduced it from 1500 to 1272 and it worked.
the problem is still that another WinXP machine has basically the same accessibility problems as the MacBook had, and there I cannot really mess with the MTU settings. Same applies for my iPod touch, which I have to jailbreak in order to mess with the MTU. Plus, the MacBook occasionally goes back to 1500 by itself, and it is very annoying to reset it every single time.
The strangest thing is that I created this ad-hoc network in the most standard way possible (using the XP wizards), without making ay funky configuration or something. Yet, as it seems, it doesn't even allow a Win XP machine to connect to another Win XP machine.
Please, help. I really need to use this laptop as a router, and currently buying a standard WiFi one is not an option.
Using ICS will create a 'router' of sorts out of your XP machine, i.e., it will assign addresses (192.168.137.x, I believe) to the clients behind it (i.e., coming over your WiFi interface), so I don't know if changing the MTU settings on your hardline router will help because it's not handing out addresses to the wireless clients connecting to your XP PC.
You may want to try Connectify (http://www.connectify.me/), if you only need wireless clients to get access to the internet - it uses your WiFi card to create a hotspot. Essentially what ICS does, but works well from my (admittedly short-term) usage.