STEP 7 V5.1 is a 32-bit application which requires Microsoft Windows 95, Windows 98, Windows Me, Windows NT or Windows 2000 as its operating system. It cannot run under Microsoft Windows 3.1 or Microsoft Windows for Workgroups 3.11.

The Microsoft Service Pack 1 for Windows 95 (Windows 95, version 4.00.950a) or at least Service Pack 3 for Windows NT 4.0 (NT version 4.00.1381) should also be installed, as applicable. MS Windows 95 requires the installed MS-Internet-Explorer 4.01 SP1 (or newer) as well. For Windows 2000 Service Pack 1 has to be installed. You can find information about these software packages on the Internet under Microsoft.

上面的是STEP7 5.1 SP4的readme中说的。
还有一点要注意的是在win2000 中安装要有管理员的权限。