Wikipedia says this is not possible since Win98 does not provide OS-level support for Unicode Indic Scripts. However, the only possible solution is downloading IE6(ugh!) or a modified version of Firefox.
For the Firefox enthusiasts, i wish to draw your attention to the following words on the site:
The patch on this page is extremely unlikely to be integrated by Mozilla. The reason is that Mozilla and Firefox are switching from their existing graphics rendering layer to a new implementation, and the patches here apply to the old implementation (used in existing Firefox versions).
Which in simple terms means that this a unofficial "patch" to firefox to help it overcome the shortcomings of Windows 98. However, although the patch is stable (which means lesser chances of Firefox crashing) it is unlikely that this change will become a part of the official Firefox installable for various reasons.