Floss,
I asked my husband about this last night because it's a problem we had some time back and I wasn't 100% sure that what I had said was correct.
To assign a static IP address to each of your machines
see here. That link only covers Windows machines - my husband said that he left the iPod Touches, iPhones, Galaxies, etc on DHCP because he couldn't be bothered to go through all that malarky as well. I would have thought that they can be assigned a static IP though because we had the Sky man out to look at our HD box a couple of months back and we got him to assign a static IP for the On Demand gizmo.
The static IP pool that we use on the servers, PCs and laptops is from 192.168.0.50 and upwards.
On the router homepage we then assigned a DHCP pool which was outside the range of anything used by any of the machines using static IPs - namely 192.168.0.2 to 192.168.0.20. That way the only conflicts that could possibly occur would be between two mobile devices themselves, and my husband figured that, if it happened, it would be far quicker to restart a mobile phone than to reboot a PC.
After doing all that, my husband seems to think that he reset the wireless mode to allow b,g and n devices and they have all been working OK together since. He also thinks that the issue my son has is that he comes back from uni and downloads torrents which flood the router and the firewall then blocks everything for 20 seconds or so, but he can't be fully sure that's what's doing it.
Capisci?