Please keep in mind this is not fool proof. Some Semprons the core is good to go, others you are in for disappointment, and the newer it is the less likely it will be to work. You need to go into your bios and look for "Advanced Clock Calibration" and set it to "Auto" then boot your computer. If it crashes trying to load windows then the core is bad (very likely) and you need to go back in and change that setting to default. You're not going to break anything, it just probably won't work.
If you do get into windows I suggest running some tests using Prime 95 for a couple hours to make sure its stable.