Sagemcom 2704N causing MacBook to crash

[#1]

I've recently set up my router which I thought was working fine until I tried to use my MacBook laptop. It is probably getting on for 10 years old and is currently running OS X 10.5.8 and I cannot phyiscally update it anymore with installing a new operating system.
The problem both myself and my girlfriend  (who is also working on a old MacBook) are having is that when we turn on Airport it literally causes out machines to start with the spinning wheel (loading wheel) and almost freezes our machines to the point where we cannot click any buttons. The mouse will move the spooning wheel around the screen but we cannot force quit anything. The only thing I have managed to do is turn the laptops off via the power button.
This has definitely got something to do with our new internet wireless router because we've never had any issues before. We are both using our iPhones with the router perfectly well. I first suspected it might be something to do with our laptops being old devices as the instructions that came with the router mentioned that older devices that we're not Wireless N compatible might have issues. Therefore I have logged into the advanced setting of the router via my phone and changed the wireless setting to the setting from the drop down which said G but still no luck so far.
I really need some advice as to whether anyone else has experienced the same problem or if anybody has any helpful advice or tips. Thanks

[#2]

You need to disable ipv6 on the macbooks

[#3]

Ok thank you this seems to be working
Not really sure what IPv6 means or does but I'm able to use my computer without feeling like I want to launch it out the window. Thank god for forums and the people that use them.
Will this affect my laptop use on any of the other wireless networks I am also connected to on this Mac? Such as my work wireless network?

[#4]

At the moment shouldn't affect anything I wouldn't have thought.
As ipv6 becomes more widespread you may have issues but that's some time away and I'd hope the routers firmware would be fixed by then..