Wireless Router Woes

[#1]

I have a strange problem, my config has a wireless router connected to my ADSL router, both are on different subnets.  This config has worked well for years, but recently my Pure Evoke flow radio started dropping connections, this device has a buffer so it had to be something serious.  It also become problematic to connect the wireless PC's; requiring a reboot of the wireless router and then it only worked for a while.
I examined the router logs and it was dropping connections about every four minutes, I could see it was issuing new DHCP leases at these intervals which matched the radio drop outs. Teh DHCP leases are set for a week so it is strange to see this loss of connection.  I figured it was an old router so I replaced it with another one I had around the place but had hardly been used.  The same thing happened.
I have no problems with the ADSL router which my desktop PC is connected to, so I am stumped.
My amateur "feeling" is that our wireless G network is being blasted by a neighbours BT router which creates the usual 3 Wireless networks as that is the only change I have seen around here. I have tried changing channels but to no effect.
Does anyone have any ideas of what might be causing these dropouts, it is weird that it is on both wireles routers?
Do I need to go get a super powerful wireless blaster beast and create enough radiation to cook a turkey whilst blasting my neighbour back?

[#2]

If the problem is related to DHCP, why not try turning it off and configuring IPs etc manually as a starting point. I had a similar problem a few years ago where the router just seemed to 'lock up' and drop wireless connections. Sometimes it sorted itself out, more often it needed a reboot. I had it down to the fact I'm surrounded by about 2 dozen wifi points, 5 or 6 of which are in the same building. Manual config seemed to do the trick and I've always used it as a starting point with any new router since, although it would be more of a pain if you have a lot of 'visiting' devices.

[#3]

Thanks for reply Mark, I tried that, the DHCP is just what shows in the logs, the connection drops every four minutes on both routers

[#4]

bump

[#5]

Is there any timeout setting on the wireless client?