Welcome to Discussions, robertkunda
Sounds like it might be interference. To help minimize interference, turn on interference robustness if it is not already enabled.
Keep wireless phones and BIG speakers or other potentially interfering devices away from the Mac and your wireless router.
http://docs.info.apple.com/article.html?path=AirPortUtility/5.1/en/ap2082.html
If that does not resolve the problem, see your wireless router device user guide (manual) if needed and change wireless channels in the router. Move as far as possible from your currently used channel.
If current channel is Auto, 1, or 6, change to Channel 11. Save the settings and test whether the problem is fixed.
If the problem persists, unless the channel was originally set to "1", change to Channel 1. Save the settings and test whether the problem is fixed. If not, unless the original channel was "6", try changing to Channel 6. There is no need to try the intermediate channels.
If your wireless router is an Apple Airport, one of these Help articles may also give you some help:
http://docs.info.apple.com/article.html?path=Airport/5.0/en/ap2072.html
http://docs.info.apple.com/article.html?path=Airport/5.0/en/ap2043.html (power setting)
If none of the above fixes the problem, the trouble is unlikely to be related to interference. In that case, the first thing I would try is connecting wife's iMac via ethernet to verify that it is reliable when connected via wire.
EZ Jim
Mac Pro Quad Core (Early 2009) 2.93Ghz w/Mac OS X (10.6.2) MacBook Pro (13 inch, Mid 2009) 2.26GHz (10.6.2)
LED Cinema Display G4 PowerBook 1.67GHz (10.4.11) iBookSE 366MHz (10.3.9) External iSight