Membership with Authorize.net issue

Hello,

When activating Authorize.net with membership > (and deactivating PayPal) the subscribe button disappears and there is no way for the user to continue?

Also we are utilizing a merchant account provider who emulates Authorize.net and need to change the POST url to emulators POST URL. Please advise where this is located and if there are any other changes needed to make it work. ( emulated authorize.net ) Of course we have entered in the supplied Gateway ID and Password - where do we get the MD5 hash from?

Please reply asap.

Thanks,
Jon