Windows XP HDD-SSD change

  Hello!

My laptop was broken so my brother was kind enough to lent me an old laptop of his for a couple of months until i can afford to buy another.The problem is it  has windows xp the hdd is slow like hell and has a few other perfomance issues and he doen't want it formated because he had this device for about 10 years or so and has loads of data in it!My question is if i replace the hdd with an ssd i have and install windows 7 then when it's time to give it back switch to the old hdd with xp will it be restored to its prior condition (functional windows xp and all)?

Your brother was very brave, lending you a laptop with data he doesn't want to lose on it. Not that I think you would have purposely deleted any of it, but mistakes *do* happen. 

Your brother  was also very brave having data he doesn't want to lose  without having any backups of it on external media. It is always possible that a hard drive crash, user error, nearby lightning strike, virus attack, even theft of the computer, can cause the loss of everything on the drive. And with a laptop, add to that the possibility of dropping and breaking it. As has often been said, it's not a matter of whether you will have such a problem, but when. 

To answer your question, yes, you should be able to do that, *if* the laptop has support for the SSD. But if I were in your shoes, the first thing I would do is back up his data to external media, just in case.