This usually is not enough installed RAM.
The best RAM configuration for Win98 is 384 Meg.
This problem is easy to troubleshoot.
Download Cacheman from www.cnet.com
(Cnet is the parent of TechRepublic.)
Look at the amount of memory used, as reported by Cacheman.
If you have no free RAM, use Cacheman to reduce the Disk cache to twice the cache on the hard drive.
In your case the HD cache is probably 2 Meg, so the settings are 4Meg Max, and 512K Min.
This is a guess based on the age of your PC.
You can find the actual amount of cache memory installed on your hard drive by going to the hard drive manufacturers' website. It is one of the specifications of the drive.
There is also a utility included with Cacheman to install settings to PCs with low RAM.
This is a temporary Band-Aid to get Word working.
More memory is probably going to be the best solution to this problem.
Note* The problem you are seeing is not an OS problem, and it is not the hard disk, unless the hard disk is full.
Regards, Chris