Cannot load CDs to itunes on iMac ( OS X v10.6.8 ). all systems updated. The CDs works in my friends cheap Dell/ windows.

Question

the discs are single, new, clean, flat and load in my friends dell/ windows fine.

Answer 1

=Troubleshooting CD ripping issues=
The easiest thing to check is if it is just this CD.  Try another one.  If others work, then it is likely the CD. Yes, evenif it works in a friend's computer.
Try an alternative ripper such as XLD or Max.  Even though you may not want that as the long-term solution it will at least indicate whether the problem is with iTunes or something else.
X Lossless Decoder: Lossless audio decoder for Mac OS X - http://tmkk.pv.land.to/xld/index_e.html
http://sbooth.org/Max/
If other CDs and rippers do not work, it could be the drive itself, or the part of the computer running the hardware. For the latter some have found a SMC reset to work.
Intel-based Macs: Resetting the System Management Controller (SMC) - http://support.apple.com/kb/ht3964
Apple Portables: Resetting the System Management Controller (SMC) - http://support.apple.com/kb/HT1411
If you think it is the drive, you can try a cleaning disc (about $10 from a computer store or media store) to get rid of dust.  I haven't had much success with these, though usually I am running some older machine on which I can expect a drive to die after 5 years of use.
If you're really desperate and none of the above work, you could look at: https://discussions.apple.com/thread/3635433 - tips on possibly repairing an old CD drive  If you have to go to this extent you're probably in a place where you just want to think about getting a new drive.