Try running
Netstumbler to see what other wireless
LANs are in range and change channel on your router/
Access Point if necessary. Note that only
802.11b/g channels 1, 6 and 11 are considered non overlapping (even though they still do) so having your's on channel 5 and the neighbour's on channel 6 (for example) will still mean significant interference. See
Wikipedia for more on this. If your microwave is used a lot then it might be worth checking the unit for the specific frequency that it operates on and then choosing an
802.11 channel as far from that as possible (e.g. my microwave operates on 2450GHz so I chose a channel away from that to avoid interference. Obviously any other 2.4GHz band equipment in your home (some baby monitors, some cordless phones,
Bluetooth devices etc.) may also interfere with your network.
Another thing to check is if there are any driver or firmware updates for your
802.11 equipment that might address outstanding bugs and interoperability problems.
One basic thing to check is that the wireless router is suitably located for best coverage (e.g. not unduly obstructed by shelves etc. and usually at a high point in the house.