Roberto is correct. Version 7.1 was the first version to not support Windows 98. CVI 7.1 itself would not install in Windows 98, but it still allowed you to create distributions for your application (via the Create Distribution Kit feature) that could be installed in Windows 98. However, with CVI 8.0 you can't even install distributions in Windows 98, since the newer installer technology that CVI 8 uses simply doesn't allow it.
So if you wanted to run your application in Windows 98, you'd have to zip up all the files you need manually -- including the CVI runtime engine -- and copy them into the target PC. But like Roberto said, NI cannot make any guarantees that the particular libraries you're using will work in Windows 98. Many probably do, at least to some extent, but they have not been tested.
Luis
NI