Bit of advice, if you have a spare PCI slot in your tower, get a wireless card not a wireless dongle. There are much fewer problems with cards and much better range. The cards come quite cheap, bought mine on ebay for £8 secondhand ages ago.
The same sort of thing with laptops, use a PCMCIA device rather than a wireless dongle.
I have ignored this advice to my cost in the past, once you get up to WPA or better still WPA2 encryption, there can be problems with dongles.
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