Hi
A few factors
1) These are the hardware requirements, your install may still work even if some of these are not met but probably not great
Hardware Requirements-
* 233 megahertz (MHz) Pentium or higher microprocessor (or
equivalent)
* 128 megabytes (MB) recommended (64 MB of RAM minimum;
4 gigabytes (GB) of RAM maximum)
* 1.5 GB of free space on your hard disk
* VGA monitor
* Keyboard
* Mouse or compatible pointing device
* CD-ROM or DVD drive
2) If you chose upgrade MS says that it should keep your existing files and application, how accurate this will be with your system I am not sure. As always backup
During an upgrade, the Windows XP Setup Wizard replaces existing
Windows files but preserves your existing settings and applications.
Some applications might not be compatible with Windows XP Professional
and therefore might not function properly after an upgrade. You can
upgrade to Windows XP Professional from the following
operating systems:
* Windows 98 (all versions)
* Windows Millennium Edition
* Windows NT 4.0 Workstation (Service Pack 6 and later)
* Windows 2000 Professional (including service packs)
* Windows XP Home Edition
I obtained the info from the readme file which came on the Win XP Professional CD