That question could spark a lot of wars... ;-) I'll tell you what I did a bit later. First thing though, to save yourself the hassle of learning a new OP SYS, have you looked into whether your old XP box would run Win7? Get yourself a download of Windows 7 Upgrade Advisor. Install and run it and it will give you a really good idea of whether you can run Win7 on your old box or not. If you opt to try out Win7 I would recommend picking up a new hard drive, install as primary and install Win7 on it. Then hook up your old XP drive as secondary and you can migrate your files from it. When you get all your stuff off of the old drive, reformat it and use as a data drive...
If the above was Greek to you you may not want to go playing around with anything else. But if you are comfortable playing around with OpSys installs and don't want to try Win7 I would suggest one of the many fine Linux distros. What I did when faced with the death of XP follows.
Three machines were affected by XP endoflife, an old (vintage 2002 or 3) single-core cpu laptop, a newer vintage dual core cpu laptop business model that came with XP back when no businesses would buy Win Vista but was capable of running Vista (note: if the machine would run Vista, chances are like 99% that it will run Win7) and an old desktop that once was my Daughters that I used as a guinea pig... ;-)
I had purchased some hardware (MoBo and dual core cpu) to upgrade the guts of Daughters old box, but instead got her an all-new quad core setup, so I tossed the new stuff into her old XP box and started experimenting with Linux distros. Finally settled on Mint with the Cinnamon desktop, and have been happy with that result. It has two hard drives in it so every new release gets loaded as a clean install on 'secondary' drive, the old primary becomes secondary, and the new install becomes the boot drive (so I could easily go back just by swapping drive cables should I want.) (Like I said, this box is the 'test bed.')
The dual core laptop got a 250G SSD and Win7 installed on it with the old WinXP hard drive stuck into an external USB enclosure until files were scavenged, at which point it was reformatted (as I said, the machine was designed to run Vista and there were no problems going to Win7.)
The old single core laptop was the biggest challenge. I was pretty sure that I could get Win7 to run on it but the performance hit would render the machine useless for more than a paperweight with pretty graphics, so I opted for Linux on that machine. That took some doing. The machine itself was maxed out at 1gig of memory of which 256k was 'shared' with the video. I copied all my Windows files off the hard drive and departitioned it so I could do a clean install of Linux. And started having issues. Apparently when you install from a DVD, the install routine loads, or tries to load, all the necessary stuff into RAM. It seems to require at least a half gig of ram to get all the stuff in, and then some left over for 'wiggle room' - operating space during install. Here's where I ran into issues with the available ram on the machine, most often after it had run the install to the point that it was trying to make the jump to running off the hard drive (following letting the install partition and format the drive and try to copy files to it.) Somewhere in that sequence I would develop a memory overflow thing and was dead. Had to play around with different versions and desktops to find one that could get through the install without seizing up. A fault of the hardware limitations on the laptop, not Linux itself - Ubuntu, Mint, and Debian all had issues at roughly the same point.
End result of all this verbage - if you can get Win7 to run on your machine, I would recommend that. If not, go Linux. Download one or more distros with whatever variations of desktops they have. All the ones I looked at had the ability to run from the DVD so you could get an idea of what you were looking at. Then pick one and install - and then start playing with it.. ;-)
Good info. I don’t get the mindset that something new is out so it is time to throw away all the old stuff. I have an old multimedia machine with XP on it. I got a Windows restore virus in it and think it messed up the video. I still have use for it to run an entertainment center.