Siegfried, i think you found these already - but here is the blog posting on how to connet arduino to nimbits.
http://nimbits.blogspot.com/2010/07/data-in-connect-arduino-to-nimbits-data.html
tublar - check out www.nimbits.com, there is a lot of client code both .net and java - it'd be pretty easy to make a buffer in your code on the lan if the internet connection dropped. I may just add that to the code library since it's a pretty basic need.
- Ben