And yet, if your program was created with Windows 98 primarily in mind, it has a reasonable chance of working in Windows 7 or 8. But if it was already old in 1998, or was written to be backward compatible back then, it will have problems with most current computers.
If your attempt to run or install the program gives you an error message that reads something like the one below, chances are you're trying to run a 16-bit program in a 64-bit environment. You can't do that.
Originally, Windows was a 16-bit environment, and ran only 16-bit software. With Windows 95, the operating system went 32-bit, and could run both 16- and 32-bit programs. Windows Vista, 7, and 8 all come (or came) in 32- and 64-bit versions (the version you get depends on your PC's processor). The 64-bit versions can run 32- and 64-bit programs, but not 16-bit ones.
To see if you're running 32- or 64-bit Windows, check your System information. To get there in Windows 7, click Start, right-click Computer, and select Properties. In Windows 8, click the Search charm, type system, click Settings, then System. Once there, look for the System type field for the answer to your question.
If you're running a 32-bit version of Windows, you may be able to run that program. Right-click the .exe file, or a shortcut to the .exe file, and select Properties. Click the Compatibility tab. Then check Run this program in compatibility mode for and select an appropriate option. Then try launching it again. You may need to go through several options before you find one that works.
But if you're living in a 64-bit world (and these days, most of us do), your choices are limited. If you have Windows 7 Professional, Enterprise, or Ultimate, you can download and install Microsoft's freeWindows XP Mode and Windows Virtual PC. This runs a copy of XP in a 32-bit virtual machine.
Unfortunately, if you're running a 64-bit version of Vista, Windows 8, or Windows 7 Home, that option is closed for you. You can download and install a free virtual machine program, such as VMWare Player, but you'll also need an old version of Windows to run in it.
Or, if you're using the 64-bit version of Windows 8 Pro or Ultimate, you can use the included Hyper-V to run a virtual machine, although you'll still need a licensed version of XP.