Had the same issue with the last few KDE installs, only wireless connection but wired is not an option here so not tested. Today came across some issues with upgrade to fedora 14 in KDE once again, works now - below is my struggle, perhaps it help ?
configured gnome wireless connection for both routers and downloaded & installed KDE 4.5.5. so close to satisfaction right...
Noticed the same settings would not work in KDE even after the all updates were applied, before attempting to connect I always go though KDE's settings menu to manually configure my personal network or the applets manage/edit connection option from the task bar since one needs a manual IP. Noticed a few caveats with this version either way and sort of put off by it consistently in various KDE versions.
1) no option to connect. I don't expect to see the hidden network but my leisure connection was present...click click .....click.
2) no settings after reboot, redo reboot gone again.
3) delete wireless connections (complete rewrite in gnome and KDE)
3) log into gnome connect... then log into KDE, Voila!! we are connected to wireless network
4) reboot, settings in KDE vanished once again, aw shucks
5) repeat steps 1 through 5 via terminal.
things are great now, cute little status monitor and all the trimmings one would expect from KDE but getting there was a pain.
In a nutshell, auto does not seem to be an option despite gnome's ability atm so your router's status page is the best resource for a manual setup