I was using ndiswrapper 1.47, and could connect to my AP without problems (WEP).
 
However, if I connected to my z555 from another machine, and did anything that caused a lot of traffic, the z555 would drop off the wireless network.  It was necessary to rmmod ndiswrapper, and restart the network (which re-loads ndiswrapper) to get it to re-connect.  AFAIK, There were no messages in the logs at all when this happened.
 
Given that large data transfers are common on a machine that is "the center of my multi-media life", this was a major problem.
 
Similar posts on the ndiwrapper forums http://ndiswrapper.sourceforge.net/joomla/index.php?/component/option,com_firebo ard/Itemid,34/ , indicated that downgrading to ndiswrapper 1.44 may help.  I tried this, and the problem persisted.
 
In a last, desperate attempt to avoid building a new kernel, I tried something else.
 
I attemped to load the Win98SE drivers, instead of the WinXP drivers. Links on my main Z555 Page:
http://linuxslate.com/Guide_z555.html
 
I had to create a link from 2802W51.sys to 2802W.sys to get it to load the Win98SE drivers, but as soon as I did so, it worked, and the z555 has not dropped off my WiFi network yet, despite several long X-Sessions, Lots of accessing Mythweb, and the transfer of 3 movies.