If I buy a voluntary,resale will it be included in my current interval account that holds my developer purchases or do I need to open a separate II account?
You must open a separate Acct., because your SVN fee pays for your developer Acct. with II, and Starwood won't permit you to put non-SVN weeks in the same Acct. Sometimes II gets confused about this issue.
However, if you requalify a voluntary resale, it will be treated EXACTLY like a developer week, and will be allowed in the developer II Acct.
See the II FAQ at the top of the forum for a walk-through.