So I just got a Dell XPS 400 for $20 off a friend of mine. I didn't really need it but I got it anyways because I thought I could upgrade the CPU in it and run Windows 8.1 and give it to my grandma for her birthday next month. She really needs a new computer because she is still running Windows 98 first edition. The motherboard it LGA 775 and I have a pentium 4, pentium dual core, and celeron that are all LGA 775 with the pentium 4 being the best at 3.0ghz. I don't really want to use the pentium d that came in the system because it's actually older than any of the other LGA 775 CPUs that I listed off. Any help would be appreciated and I don't want answers like don't get a Dell or buy a new PC, because this PC would be like new to my grandma coming from windows 98. Thanks in advanced!