Aye, just because you have a 10/100 NIC doesnt mean that your cable or T-1 line will give you 10/100 speed.

If they are on the same intranet then you will get the 100 speed and all is happy. Since it sounds like you will be going thru cable or a T-1 line, you are at the mercy of your provider.

If the computers are both in the same data center, then they are on the same intranet.
If the computers are in seperate data centers, then they are seperate intranets and once you have the VPN in place you can transfer data between the two servers, but the max speed will not be 10/100.. it will most likely be 900kbs - 1.3mbs depending on your connections to the internet at each location.

Unfortunatly, it will be based on the slowest link in the chain.