Sounds like you do not have enough resources for all the tasks that you are trying to run at once.
For Windows 9X / Me systems, you need the following:
128MB to 384MB of system RAM
1GB free hard drive space.
If you are running a fix size page file, I would increase it's size to the difference between 1GB and installed RAM.
For Windows 2000 or XP:
256MB RAM - Minimum!!!
2GB free hard drive space.
For Windows 98 and Me, you can also have a memory leak problem.
I have seen IE 6 cause problems for many systems with W98.
Similar problems happen when you update to DirectX 9 if your video card driver does not support it.
Check for an updated driver for your video card.
It would not hurt to disable as many programs in the system tray as possible.
Also, download and run AdAware from www.lavasoft.de
If you are still having problems, download and run one of the memory managers from www.nonags.com
Chas