When you ask a question regarding ISA client types, you need to understand that there are three types of ISA clients:
Web Proxy Client
The SecureNAT client does not require client software installation or configuration.
The Web Proxy client requires that the Web browser be configured to use the ISA firewall as its Web proxy device. You do not need to install any client software
The Firewall client is a Winsock Proxy client (similar to a SOCKS client but infinitely better) that provides transparent application proxy services to the ISA firewall’s Firewall Service. The Firewall client software must be installed and configured.
MORAL OF THE STORY:
Do not refer to "ISA Client". Be specific regarding the client type you’re using.
Thomas W Shinder, M.D.
MVP -- ISA Firewalls