1. yes, you can use Cisco VPN client software to connect home users to PIX 501.
2. Since the home users get their ip addresses through ISP's DHCP server, you will have use an user id and password to identify the user. Obviously the ip address that you set on the vpn client is always the same (probably the external public IP address of the firewall).
3. You can download the vpn client software if you have cco id - free of cost.
send me an email if you need further details : sampathsr@yahoo.com.