If you have a google hosted gmail account like nameschool.edu it says here https://www.google.com/a/edu/ that you will be able to access Gtalk Gmail and Gcal but will you be able to use that email address as your main google account and sign up for services like writely, etc?

Yes, since you can sign up for a Google Account with any email address you would be able to do this but they wouldn't be linked. This is possible because they use totally different login areas and accounts.

BTW, you could then have a "Google Apps" calendar and a "Google Accounts" calendar – and also a "Google Apps" login for Google Talk as well as a usual "Google Accounts" one (since a Gmail account is no longer required).

Yeah, I have two. One for my business

https://www.google.com/a/netterbox.co.uk/ServiceLogin?service=mail&passive=true&rm=false&continue=http%3A%2F%2Fmail.google.com%2Fhosted%2Fnetterbox.co.uk&ltmpl=cm_googlemail&ltmplcache=2&hl=en

and one for my personal. They're completely separate.