How do I stop Mac OS X from creating .DS_Store files on WebDAV upload?

Open a Terminal and execute:

$ defaults write com.apple.desktopservices DSDontWriteNetworkStores true

This will turn off writing these files to all network volumes.

More information on this subject can be seen here:

http://docs.info.apple.com/article.html?artnum=301711

As per the linked document, preventing Mac OS X from creating .DS_Store files can have adverse effects.