I am a fresh developer on Googles Android Platform - my HTC Desire arrived last week.
Now i need a way to sign in to my existing application (Java, currently running
I'm not sure I understand where you want the user to be logged on.
Note that you can't assume which web browser will be used (default browser, opera mobile, manufacturer browser, etc.) If you only offer an web site, it is the web browser responsibility to know the user. Most people I have already logged in their google account. Android is sort of unrelelated here.
If you want your Android application to connect to a web service without prompting for a login/password, you can't achieve this with openID. I suggest oauth for this use case.