I have plenty of space on my hard drive (500GB), but when I plug in my iPhone there is a window stating the pone cannot be backed up because of lack of disk space. The same occurs with attempting to import CD's into iTunes.

How much free space do you have?

If you click on your Hard drive icon (should be upper right hand corner of your screen), or the Finder in your Dock...when the window opens it says at the bottom how much Free Space you have on your drive.

How much space is available on the phone?

Oh I see you have the issue on importing CDs to iTunes also. Strange.

I would seriously consider running Disk Utility:

Applications > Utilities > Disk Utility

and scan the hard drive and see if any errors are reported.

Since the Verify just checks the drive, try using Disk Utility to actually do a Disk Repair, as shown in this link, while booted up on your install disk for OS 10.6.8 and under. If you are running 10.7 or 10.8 run Disk Repair from Disk Utility on your Recovery System. It shows you how in the link.

You could have a little directory corruption that Verify missed and Disk Repair may fix. Let us know what errors Disk Repair reports and if DU was able to repair them. This could just be a start in repairs and you may need a better utility to finish the job.

Then Repair Permissions.

No need to report any Permissions errors........we all get them.

 DALE

Boot up from your Snow Leopard Install DVD while holding down the "c" key.

Select the language you wish to use, and then choose"Disk Utility"from the menu bar.

Your HD should appear in a panel on the left hand side of the window which opens. Select it and then click on the"repair disk"button in the right hand section of the window.

If Disk First aid is unable to complete the repair you will need to use a stronger 3rd party utility like DiskWarrior or TechToolPro.

Once this process has been completed restart your computer.

Utilities & info regarding checking your HD space: