It depends very much on the hardware. You are going to have to see if drivers are available for that specific hardware in newer versions of Windows. My guess is no, you are out of luck with Windows. Perhaps this PC would be a good candidate for Linux?
You would need to supply more information about the items you wish to run under Windows 7 - most likely there will be no driver support, however it is possible to run some XP drivers - albeit with a performance hit and stability hit
I'm a little surprised at some of these answers. There is no way a windows 98 machine runs 7. Forget drivers. The hardware from that era wasn't fast enough and didn't have enough RAM. People, those were pentium II's with 256mb of ram. It isn't happening unless somebody stuck windows 98 on a newer machine years after it was obsolete.
I haven't used a real windows 98 in over 10 years, so i forgot how little RAM capacity they had. You can still run a half decent Linux distro though. Maybe Windows XP for that matter, who cares about the support anyway. Theoretically that would mean that windows xp is even more safer now since it doesn't need to send data to Microsoft. You can still have anti-virus programs installed but you have no concern when using linux about that matter.
There's 2 ways to make it run win7/vista.
1. upgrade the RAM to 2GB if possible
2. Use Readyboost™ on a SDcard or USB, If Vista or newer is installed.
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Option 2 is very, very slow. But better than nothing.