I haven't actually been able to generate a Thrift client for C# directly. However, there are some pre-built clients for Cassandra out there on the web you can already use. You will need to regenerate them if you switch versions of Cassandra.
I started with Aquiles which wraps lots of the thrift functions in their own class library. After looking at what Aquiles was doing, I wasn't happy; it was hiding a lot of stuff in Thrift that is available, and using the underlying thrift client isn't that hard. It will also teach you about how Cassandra works if you use the Thrift client.
Fortunately, part of the Aquiles client download contains a compiled Thrift client. You can just reference that in your project and that should be enough.
There are two dlls you need to reference:
Apache.Cassandra.064.dll
Thrift.dll
The 064 is the version of Cassandra you are working with.
Next I'll reference some articles on how to setup a local instance of Cassandra running on your own machine.