iMac dropping internet connection

My iMac keeps dropping the wireless internet connection and then picking it back up every 30 seconds - 1 minute. The airport bar does fluctuate from a full to half signal during the 30 seconds it is connected.
My laptop (pc) works 100% with the connection and never drops it. I even lugged my hefty 24" imac downstairs, plugged it directly into the router and that worked fine, so I have eliminated the actual connection itself.
I have done a system update, all updated.

My router is a Netgear WGR614. I have also moved my router around to see if the signal strength is increased or, the connection drops. The same happens wherever I place it. It's a new problem and I have used the router fine for the best part of 3 months before this happened.

Can anyone help me out?

Are you running Leopard 10.5.2? There are a lot of wireless issues with it. I think you have the same router I do or close to it, so I know it has a problem with my iMac on 10.5.2. I downgraded back to 10.5.1 myself to fix it.

Yeah I am. How do I go about downgrading my version?

Truth be told, i'd love to go back to tiger, it's just a shame that there are only two features of Leopard I have become dependent on!