There is not a lot you can do to speed up a Windows 98 PC, it will not recognize a dramatic increase in RAM or CPU speed due to it's coding, the only way to get good results would be to format the machine and put Windows 98 back on.
If you wanted to buy new hardware to attempt to increase the performance make sure you check the maximum specs that Windows 98 will accept, the parts will also be fairly expensive as it's so outdated and no longer in production.
It might well be worth getting a new machine, reasonable units can be found cheap and there are serious security flaws with Windows 98 being on the internet, it no longer receives windows updates and will not get any security patches.
Teris
April 2010