Unless Apple sold I-Photo to Adobe, you need to ask in a Mac forum
Highly suggest using the Adobe Aperture plugin that was released a few weeks ago do move your library. Best practice would be to:
1) backup your iphoto or Aperture library
2) convert to Lightroom
3) validate you have all the information/data/files you need/expect
4) WAIT several days or weeks
5) reevaluate if you have everything you need
6) delete your old iPhoto or Aperture library
7) use the "find missing photos" command (or whatever it is) in Lightroom to make sure you haven't deleted any images it is referencing
Not sure about iPhoto, but the Lightroom plugin will copy any files that are "managed" (within the Aperture library package), and NOT COPY any files that are referenced (lie outside the Aperture library package). Therefore, it would only be safe to delete the Aperture library when complete, not any externally "referenced" images. See #7.
Unfortunately, a backup is your best bet, and keep it for as long as you feel necessary. I've had to go back several years to my CrashPlan backup to find missing images here and there.
Thanks for the detailed reply photo-enthusiast. I think possibly the most important piece of advice you give is to wait several days or weeks. Acting impulsively could, on reflection, be disastrous.