If both your Win Pro and your friends' Win Home are directly connected to the Internet (not behind a Broadband router like Linksys/D-link),it's very easy.
Quote from Windows XP Pro help and support centre:
By creating an incoming connection, a computer can act as a remote access server if it is running Windows 2000 Professional, Windows XP Professional, or Windows XP Home Edition, or if it is a stand-alone computer running Windows 2000 Server. You can configure an incoming connection to accept the following connection types: dial-up (modem, ISDN, X.25), virtual private network (VPN) (PPTP, L2TP), or direct (serial, infrared). On a computer running Windows 2000 Professional, Windows XP Home Edition, or Windows XP Professional, an incoming connection can accept up to three incoming calls, up to one of each of these types.
The Multilink feature automatically configures multiple modems or ISDN adapters for use with incoming dial-up connections. For more information on Multilink, see Configuring multiple device dialing.
When you create a connection, the users that can connect to your incoming connection and their network protocols are selected. Each user that connects to an incoming connection must have established a local user account. For more information about user settings such as name, password, and callback rights, see To grant incoming connection access rights to your computer. For more information about configuring your connection for the TCP/IP network protocol, see To configure an incoming connection to use TCP/IP. For more information about configuring your connection for the IPX network protocol, see To configure an incoming connection to use IPX. The IPX/SPX protocol is not available on Windows XP 64-Bit Edition.
For information about creating an incoming connection, see To make an incoming network connection.