Hello lfhos. Reformatting your hard drive and installing a new operating system MIGHT resolve your problem. It is a drastic solution and going from ME to XP could bring on a number of new problems. To make sure that your system can run XP see this site for information regarding what system hardware is required to use XP:WinXP Home System Requirements
Regarding your graphics card, you will not be able to use your current ME drivers with XP. XP comes with drivers for many hardware devices but it is not guaranteed that the drivers for your particular card will be included. Here is a link where you can download the correct NVidia drivers for any Windows operating system:NVidia Drivers
Find the correct drivers for your card and operating system and download them for installation.
Your freeze-ups may be due to viruses or malware on your computer and if so you can have an expert here review your system with you and help you remove it. See the link below for information on how to create a HijackThis log and post it to the proper forum for review:How to submit a HijackThis log