The Imprimatur... software is written in the Java language and it is delivered as an applet. This means that it loads in your browser -- provided that the browser has an appropriate Java plug-in and is configured to be Java enabled.
The version of the Java plugin matters. More recent versions support a Java toolkit called "Swing" which is used extensively in Imprimatur..., so you may need to upgrade your Java plug-in to make Imprimatur... work well.
Users of Microsoft operating systems may have an older version of Java pre-installed. But this version does not reflect the many improvements that have been made to Java in the last six years.
The Microsoft variant of Java is not compatible because it is woefully out of date. Consequently, you may wish to switch to a standards-compliant browser such as Firefox or Mozilla while using this site. Both of those browsers are pretty good at guiding you through the process of acquiring the Java plugin if you don't already have it. The Sun Corporation provides the Java plugin for free. Mac OSX users will find that Java is already integrated into the operating system.