How do I subscribe tweets to google reader?

[Peter]

It's not whether you're authenticated or not. For Google Reader to subscribe to your twitter RSS feed, it needs to be authenticated as well - that is, Reader needs to be able to authenticate as you.

Google Reader doesn't natively support that. But there are other RSS services around to let you work around it. Basically, you give them a feed that requires authentication, and they provide you with an unauthenticated feed containing the same information. Have a look at the link in my sources for an example. But beware that using a service like this means you have to give them your twitter username and password.