ISA in SBS - yes, it's secure
You can remotely manage ISA from your workstation by installing the MMC. To use this method the workstation has to be local. (yes, it can be done remotely from a non-local PC too but that's another blog entry.)
Insert SBS 2003 SP1 CD #3 into the workstation CD Rom drive. Browse to ISA2004 folder and double click the auto run setup.exe file. Going through the installation you'll be warned that you can't install ISA Server on XP or what ever workstation operating system you are using. Just OK that message, we aren't installing the OS, just the management console. Once past that you'll see the list of components to be installed. The only one not X'd out should be the management console. Continue the installation. At then end check the box to start the MMC now.
Once in the MMC right click at the top of the left hand pane and select Connect To... enter the name of your SBS server.