You can use
Microsoft Office XP Pro - Win98/ME/NT4/2K.
Buy it from $257.20
However, there are free alternatives that work on Windows 98.
Unfortunately, the most popular, OpenOffice.org, isn't supported by Win98.
Here's a list of freebies. You can find more on
Google.
Depends what you need really. If you just want something like Word, there's many alternatives.