First of all, in your start menu, in the programs submenu there is a folder called 'startup' - delete anything in there that shouldn't be there.
Then select 'run' from the Start menu and type 'msconfig' and hit return, In the dialog that pops up there is an option to delete any startup entries which load through the registry.
I don't have a machine with Win98 installed at the moment to confirm for sure but that should be the easiest way to get rid of them.
Hope this helps.
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