You're not alone in wondering about a switch to a different band -- at the last count I detected 33 other wireless networks in my immediate neighbourhood (outer-London area with many studio/bedsit apartments). I gather that it's not just networks causing problems either -- I can detect music servers and there's probably the usual mess of cordless phones and video senders.
If you can afford to buy alternative wireless networking equipment I suspect you'll enjoy some improvement.
Before you invest, do try the usual tricks with your Belkin stuff of experimenting with different channels, raising the router above furnishings, moving the computer close to the wall adjoining the router.