You also need to see if your computer and all its components are XP compatable - not all that came with W98 are.
Windows XP Pro Advisor (will inform you if Win XP Pro will be able to be installed on your computer)http://www.microsoft.com/windowsxp/pro/upg...ng/advisor.mspx
Windows XP Home Advisorhttp://www.microsoft.com/windowsxp/home/up...ng/advisor.mspx
I agree that you should buy a retail version of XO Pro as acklan advised but whether you buy Pro or Home buy a retail version - not an oem version.
The simple reason for that is that the computer you are going to install it on is old, and if you get the oem version which is cheaper, you will not be allowed to transfer it to another computer (or motherboard for that matter).
Pro is far more capable as far as security goes and has five more years of Microsoft Extended Support (critical updates, etc) than Home will have, so that alone makes it worth the difference in price.