iLife DVD won't install on G4

I have iPhoto2 on my 5 year-old G4, and use iPhoto4 on my 2004 iBook (it came with it). I would like to have the same version of iPhoto on both machines, and sorry Apple, but I cannot afford 2 copies of iLife5 right now. So, I bought a copy of iLife on eBay from someone who had upgraded to iLife5. When I try to install from the DVD, I get this message:

iLife cannot be installed on this computer.
This installation cannot proceed because one of the following applications is running:
GarageBand
iTunes
iPhoto
iMovie
iDVD
Please quit these apps before installation.

Nothing is running. I restarted, but same result. When I try to install from the CD, it tells me to install from the DVD. What do I do now? I have upgraded to iTunes5, but I still have the version of iMovie that came with Panther, and neither is running when I try to install. I do have iPhoto Buddy. My G4 meets the RAM and MHz requirements on the iLife box.
Please help; I really just need to install iPhoto4, I don't care about the other apps.