Try running this test(http://www.pcpitstop.com/xpready/default.asp) on the 98 machine. It should give you idea if any bumps are ahead.
"What is the min and max. ram I should run with either system?"
512 seems to work best with XP, but check if your board can handle it. Win98 hits a wall at 512.
I am presently running windows 98 se on a machine with 700 MHZ and 384 MB of ram. Can I up grade to Windows Xp?
If so,what are there any concerns?
What is the min and max. ram I should run with either system?

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