If your building a ZIGBEE or any other wireless network at 2.4ghz, a major consideration is through put of data and integrity of the wireless link.

Its a good idea to use a spectrum analyser to ensure that your locality is clear of potential killer interferance such as baby monitoring devices, leaky microwave ovens, wire less video camera's and wireless alarm modules, all of which can cripple zigbee or 802.11 network performance

Take a look at www.wi-spy.co.uk

Here is a little video that explains the project range

for home users there is a low cost option: http://www.crownhill.co.uk/product.php?prod=2139

Seriously worth the money, even we cleared up a rougue 2.4ghz signal radiating intermittantly accross the band, without wi-spy we'd probably never have found nit......even though we have a 30K GBP Agilent spectrum analyser sitting in the workshop, wi-spy is just so convienient.