I haven't had much experience with Viewpoint, so i will not be much help there. However, i'd like to offer some suggestions with the IT/networking side.
I would recommend setting up some type of VPN on your network. This will add a little extra security so that ANYONE on the internet cannot access your process line. If you set up a VPN, your users will have to log into the VPN and it will set up a virtual connection to your LAN over the internet. Then they can access anything they need to just as if they were connected locally at your plant. A VPN also has many other uses, such as giving you the ability of remote programming.
Another problem you may have is most of the time DSL accounts have static IP address, meaning they change over time. You can call your ISP and ask if they will provide you with a Static IP address (for an extra fee of course). Another option is that there are several companies around that automatically update your IP address to a DNS hostname (One company is dyndns.org) This way all you will have to remember to connect to your VPN is "mycompany.dyndns.org" instead of the constantly changing "123.456.789.012". Some of these services are free or you can buy custom services for a little bit of money a year.
If you work for a company with an IT department, you will defiantly want to get with them. Most companies have a vpn already setup and you may not have to do anything but get the Rockwell software up and going.