I was looking at purchasing the 'Power' plan with it's 5 domains so I can combine a few small sites. The domains currently have their DNS records hosted elsewhere (register.com I think).

Would these zones need to be transfered to you guys? Or can I just point the A and MX records to the public IP address provided by you guys?

How does hosting 5 domains on one account work? Does each domain have a separate IP address/entry point for web, ftp and mail traffic?

Thanx.

Would these zones need to be transfered to you guys? Or can I just point the A and MX records to the public IP address provided by you guys?

Yes you can just point A records for yourdomain.com www, ftp, mail subdomains to our ips and configure MX to be yourdomain.com

How does hosting 5 domains on one account work? Does each domain have a separate IP address/entry point for web, ftp and mail traffic?

No ip based hosting is prohibited by arin.net (ip registry) because of teh lack of ips. And those providers who found to allow ip based hosting won't be assigned any ip space.

So we give ips only for nameservers and SSL. In this cases it meets Arin justification policy.

So all your domains will point to the same ip and just will be distinguished by web server through virtualhosting feature.

You can add ectra domains using Addon domains icon in your control panel.