Top Law Schools

So I'm starting my Americorp appointment tomorrow and am wondering if I should put it on my resume for the application I'm submitting tonight. Also, should I list what I expect my responsibilities to be in the past tense or preface them as anticipated responsibilities?

They probably aren't going to see your resume until after tomorrow, so just list tomorrows date until present. List your job responsibilities, if you already know them, in present tense. That is what I would to at least.

I would not list your responsibilities in past tense because at the time you wrote it, you hadn't done any of those.
Either write it as present tense or "will be managing creation of xyz website" or whatever in future tense.
(Even though they might not read your resume for a week or month, they will see that your start date was earlier and will understand that you prepared your resume in advance)

Why don't you just wait for a day or two?

There is no need to identify the day you started your assignment, just denote Americorps (September 2010 - Present).