Hmm, ok. Can I ask why?
I've been able to do this at previous hosts, and when I ran my own server. There wasn't a performance issue, and since I'd be paying for the total space and bandwidth anyway, I can't see why this is a problem.
I will never need all the space included with even the basic reseller account, but I do need to manage three domains from the same web space. Is it possilbe to have WHM added to a normal virtual hosting account as an extra?