7 years old components are just waiting to go boom. Getting Windows 7 is fine now that it's still available, but installing it to the old computer won't necessarily work. Win7 64 will work with as little as 2 GB of RAM, 4 being the minimum for fluent computing and 8 being the sweet spot. Your motherboard may not even support installing more than 4... You'd only be building bottlenecks by installing it. Stick with XP as long as the hardware lasts or you're happy with the performance, then get a totally new rig for the next seven years.