I believe that you need to do 3 things:
Add RAM, W98 works 'best' with 196MB of RAM.
Get a newer video card.
Speed is not as critical for non-game applications, as having 32MB of RAM.
Cleanup your hard drive.
Run Spybot Search and Destroy to get rid of hidden applications that are eating up resources.
Clean out the C:\Windows\Temp and Temporary Internet Files folders.
If you have IE 6 installed, that may be at the root of the problem.
I have seen W98 have enough problems with IE6 that I no longer install it on W98 PCs.
You can try one of the free memory managers as a work-around.
There are a number of them listed at www.nonags.com
If you do have a memory leak / resource issue, you may have to bite the bullet, and perform a clean re-install of Windows.
Sad to say, but the registry grows over time and can really hamper the operation of your PC.
Chas