(The latest version of this document is at http://www.milkywaygalaxy.freeservers.com. You may want to check there for changes).
Most of the companies in USA and Europe provide "Remote Access Servers" (RAS), so that their employees can dial-in from remote locations either from home or from field. RAS servers are generally Linux RAS servers or MS Windows NT RAS servers.
Nowadays, Virtual Private Network (VPN) is becoming quite popular because it supports broadband and may eventually replace dial-up networking which is very slow running at 56KB/sec. See the VPN HOWTO and VPN-Masquerade howto and java based MindTerm-SSH-HOWTO.
Configuring a dial-up connection on Linux is about as simple as it is in Windows. We will use PPP.
Definition: PPP ('Point to Point Protocol') is a protocol, that makes it possible to make IP-Links (Internet Protocol) between two computers with a modem.
The operating system Linux has this protocol in the kernel (If you compiled it into the kernel). For a ppp-link you need to start a daemon called pppd.
With PPP you can make a link between two hosts which understand the protocol. A link between a Linux host, acting as client and a Windows NT server, acting as server, is called a (Microsoft term) 'Remote Access Service' (RAS) link.
First, see if your modem is supported by linux. Internal Modems (WinModems) may work with Linux because they need extra software drivers to make it work with Linux. Test your WinModem to see if it works under Linux. Some WinModems require special tweaking to make it work in Linux.
Check if you have all the needed hardware, software and data and hand: