Multiple tiers are recommended in this kind of applications.

1. Application interface - VFP or Browser

2. Web Services - C#.NET
--- connects to Oracle through direct TCI/IP or localhost

3. Oracle Database Server

Virtual Private Network can also be used but if it uses a slow internet there will be problems on connections unless you get a exclusive leased line.

ASP.NET with AJAX technology has been around for several years. This is what I will recommend when your network goes beyond your local area network. Use your legacy system inside and expand it using Internet Browser technology beyond your TCP/IP.