You can use the link below for details on how to create a dual update profile for Eset v3 and v4 clients.
ESET Knowledgebase - How do I create a dual update profile configuration with ESET Remote Administrator? (3.0)
The Eset Remote Server (ERA) will download and provide the clients with the AV definitions, the ERA will download them from the internet using port 80, it can then either provide the updates to the clients either via http, default port 2221 (preferred method as no shares/premissions need to be set) or via file share. The clients by default will check for updates every 60 minutes from power on.
Depending on how many clients (>600) you have it may be better to provide the clients definitions via IIS as this can handle a lot more http connections than the Eset built in http server.
ESET Knowledgebase - How can I set up Microsoft IIS as an ESET update Mirror server?