[Mr Gee]

Sounds like your dropouts could be due to interference. See the text below which I copied from an online support forum:

Symptoms that may result from interference include slow connectivity, link instability with frequent disconnections and a long time to associate. Check the Link Quality indicator on the utility: if it is poor or keeps jumping up and down, it could be due to interference. Interference may be caused by other WLANs in the viscinity, and also such devices as baby monitors, some cordless phones -those operating in the same frequency range as 802.11g/b products (2.4Ghz)-, and Bluetooth devices. In most cases, such issues may be resolved by experimenting with channel numbers on the router, and see which one works best there are 13 available channels in the UK, and an interfering device is unlikely to affect them all at once. In case several Wireless LANs are present in the same environment, channels should be set as far apart as possible, given that out of the 13 channels, 3 do not overlap: they are 1, 6 and 11 -so 2, 7, 12 and 3, 8, 13 will also be optimal combinations-.