Yes, I have to use c#, it's imposed in my project.
Personally, I preferred Java because I know much better, I used it during my studies (now I'm learning c # at the same time I'm coding my project :-))).
So I have to implement the Gnutella protocol myself in c#. Actually I only implement the principals messages based on the RFC. After, depending on the time I have left, I will see some advance fonctionnality, like GGEP implementation, etc...)
But once I finished my project (if I finished once :-))), I'm interesting in working on a gnutella project, to improve my java and protocols knowledge and participate in a open source project.