All you can do is install it and see if it works.
The documentation was produced prior to the platform being tested (6.01) or certified.
The 6.1 version has a support statement in the release/readme notes. If it doesn’t work after you install, then the next step is to log a service request containing the issues. The worst case scenario is that webMethods will respond back with a position of non-support for 6.01 on Windows 2003 Advanced Server.
I do know that it works well on Windows XP.
HTH,
Ray
#webMethods#Integration-Server-and-ESB