Assuming you’re using .NET 3.5:
dic.Keys.First();
Note that there’s no guaranteed order in which key/value pairs will be iterated over in a dictionary. You may well find that in lots of cases you get out the first key that you put into the dictionaries – but you absolutely must not rely on that. As Skirwan says, there isn’t really a notion of “first”. Essentially the above will give you “a key from the dictionary” – that’s about all that’s guaranteed.
(If you don’t know whether the dictionary is empty or not, you could use FirstOrDefault.)