As long as your PC is relatively modern - newer then a P2 - any PSU will fit {asssuming you have a standard ATX case, which is a safe bet}.
Most of 'em now have the 24 Pin ATX connector, and the extra 4 pull off the connector so it can easily be used if your board only has 20 - you'll see straight away.
All connectors are pretty standard, and will only go in 1 way so you can't get it wrong! You'll generally have quite a few "left over", so tuck them out of the way {on top of the Optical Drive is where I stuff them, but it depends on how your PC is put together}.
If you take your time, and use a few Cable ties, you'll end up with a nice neat job! It's also a good time to blow out any dust that may have accumulated.
