Upgrade from 2000 to Windows XP

Please help! I don’t normally upgrade anything. I buy new and get whatever op system it has on it. This time, I don’t need a new computer, but need to upgrade from Win2000 to XP for other software programs I need to use. Do I really need the UPGRADE version or would it really be better to get the full OEM version? Will the OEM version still maintain all my current data that I have saved on my system?
Thanks for the help.