I would save all my data on a external drive. Completely wipe / format the main drive. Do a clean install of Windows 8.1, then transfer saved data. Or you can install a new hard drive, install Windows 8.1, then transfer your data to the new drive. You will then have a backup drive running a outdated OS with this choice.

Windows is Windows - Western Digital isn't going to waste their time with a statement of support for a OS that hasn't been supported in 6 years. Any external hard drive is going to recognize any version of Windows, but XP is dead in the water, time to update your OS or get a new machine. I've already recycled several machine of the xp / vista vintage.

I have a PS3 that was originally a 80GB drive. I purchased a 2.5" Laptop Western Digital Scorpio Black 250GB couple years ago, followed a U Tube video for some brief & easy instructions. There is a hatch at the end of the PS3 - about 3/4" wide - 4" long , carefully use a small flat blade screw driver to pop it loose. One screw usually holds the hard drive caddy in place, there is a little handle to pull the unit out. Just swap out the hard drives , reverse the procedure & slide back into the PS3. Carefully replace the one screw, don't lose it inside. Plug in, turn on PS3, it will ask to format the new drive, select okay. I already had a PS3 account that had my game updates / saves stored in the cloud. I believe a had to download a firmware update from the SONY PS3 website, save it on a usb thumb drive and upload into the PS3. Sounds like you are starting from scratch with the game updates & saves , so it will be an easy task. The 250GB is alot of storage but the prices have come down and larger 2.5" laptop hard drives are available, Western Digital is the best out there , with a great warranty. You can check with your local Best Buy / Geek Squad for any further details.

Some laptops come with a HDD caddy or an adapter mount that you have to remove mounting screws to install the SSD. Manufacturers match up the mounting screw holes for almost very application. I've mounted some HDD / SDD's directly under a hatch in the bottom with hardly any hardware transfer. Couple screws, or a small bracket. Most of the current SSD's are 7-9mm thick the thinner being used for the very thin laptops & being a lower profile. Most manufactures will include some sort of filler gasket that will keep the SSD contacts aligned, And uses up some of the extra space. I've replaced drives in 7 - 8 laptops , and every one has been different.