Yes.
It only takes a few minutes. I'll give you a quick rundown:
1) Take off the side and plastic air dam on your PowerMac.
2) Under the existing drive, you should see two small latches. Pull them towards you.
3) Slide the existing drive out, disconnecting the three cables in the back (all of them are different sizes, so replacing them should be easy)
4) On the bottom of the drive you removed, there should be four black rubbery screws. Remove them, and put them in the same place on the new drive.
5) Using a paperclip, use the emergency eject pinhole on the new drive, then remove the plastic bezel on the front of the drive tray.
6) See if the new drive fits in your Power Mac. If it does, skip the next step.
7) Remove the plastic bezel from the front of the drive (the whole drive... not just the tray).
8) Reconnect the cables and put in the new drive.
9) Snap the retaining latches back in place.
10) Replace the air dam and side of your Power Mac
11) Power on the Power Mac and make sure you can read discs (try a data disc, DVD, and CD to be sure)
