Wireless on Imac intermittent

Having some problems here with my Imac.

Every so often my connection drops. It'll happen typically once an hour, for about 5-10 mins at a time. It's a 20" Imac intel, connecting to a D-link wireless router.

Most of the time if I switch airport off then on again, it'll wake up. Sometimes it can't find the router though so i have to wait.

I'd definitely be blaming the router if it wasn't for the fact my wife is sitting 10 feet from me with her Compaq notebook, and has a completely reliable connection via the same router.

So, other than run an ethernet cable and use a hard connection (I'm on a different floor to the router, so will avoid that like the plague), is there any tweaking I can do to get my airport card to connect better?

TIA.

Most of the issues are when channel selection is set to auto if you manually
select one from 1 to 11 in the router this problem goes away. Also it would
be a good idea to download i-stumbler to find the channel with the least amount of traffic and the best signal to noise.