Most likely a memory issue - how much have you got and how much is being used by services and other programs? And what services are running?
Can you post the machine specs please? Particularly the memory, and whether the video uses dedicated or system ram.
The fact you are connecting to a network printer attatched to a win98 machine really should not impact on performance at all unless you are printing at the time. Do check both machines for viruses, adware and trojans though.
Is the slow responce limited to Excel or is it system wide?
You mention when going to 'font' things are slow. How many fonts do you have installed? If there is a printer monitoring program on the XP machine try and disable it.
Sorry to answer your question with other questions but we've not got a great deal to go on there.