Yes, by "recovery" I mean DR III or DW, and yes, typically you run these programs from another disk/computer.
Probably you should go to the DR III and DW sites and explore.
But basically the idea is that DW attempts to "fix" your disk, so that if it succeeds, then you have a working disk. That's why they don't give you a free trial -- if it works with the free trial, then you're done and have no motivation except conscience to pay for a working version.
DR III's procedure is to extract data from the bad disk and reconstruct that data on another disk. So you can see that for them, a free trial makes sense provided they limit the amount you can transfer. DR III lets you see whether it's going to work for you or not. If it does, you pay.
In both cases, you don't want to be running the programs from the very disk you're trying to fix.
Maybe others will amplify what I've said. I can say that the times I've successfully used either program, I've always run them out of a separate computer, either mounting the bad disk via firewire in Target Mode while it's still in the other Mac, or by removing the disk, putting it in an enclosure, and mounting it that way.
Actually, the last DR III rescue I did (on a machine that was identical to your iMac) went like this:
1a. remove the bad disk from the iMac
1b. install a new drive in the iMac
1c. start installing Lion on the fresh disk in the iMac
and while that was running,
2. connect the ex-iMac bad disk to my MBP as a USB external drive
3. use DW, running on the MBP, attempt a reconstruction.
4. DW fails to recover the data, so
5. download DR III
6. attach another external to the MBP
7. run DR III on the MBP, in test mode; tell it to extract from the bad drive and put what it extracted on the other external
8. success!
9. Pay for DR III, and repeat step 7
10. attach the external on which DR III had put the recovered data to the iMac
11. from the iMac, poke around the external drive and move the desired files and folders to the iMac
12. done
The only reason I tried DW before DR III was because I already had DW on the MBP, from the last time I'd worked with a bad disk (and DW had succeeded).
In your case -- if you don't have access to another Mac on which to run either recovery program -- you'll have to change out the iMac disk and get a fresh copy of whatever system you're using there on it, and only then drop the bad disk in an enclosure, connect it to the iMac, and get to work.
Probably you should go to the DR III and DW sites and explore.
But basically the idea is that DW attempts to "fix" your disk, so that if it succeeds, then you have a working disk. That's why they don't give you a free trial -- if it works with the free trial, then you're done and have no motivation except conscience to pay for a working version.
DR III's procedure is to extract data from the bad disk and reconstruct that data on another disk. So you can see that for them, a free trial makes sense provided they limit the amount you can transfer. DR III lets you see whether it's going to work for you or not. If it does, you pay.
In both cases, you don't want to be running the programs from the very disk you're trying to fix.
Maybe others will amplify what I've said. I can say that the times I've successfully used either program, I've always run them out of a separate computer, either mounting the bad disk via firewire in Target Mode while it's still in the other Mac, or by removing the disk, putting it in an enclosure, and mounting it that way.
Actually, the last DR III rescue I did (on a machine that was identical to your iMac) went like this:
1a. remove the bad disk from the iMac
1b. install a new drive in the iMac
1c. start installing Lion on the fresh disk in the iMac
and while that was running,
2. connect the ex-iMac bad disk to my MBP as a USB external drive
3. use DW, running on the MBP, attempt a reconstruction.
4. DW fails to recover the data, so
5. download DR III
6. attach another external to the MBP
7. run DR III on the MBP, in test mode; tell it to extract from the bad drive and put what it extracted on the other external
8. success!
9. Pay for DR III, and repeat step 7
10. attach the external on which DR III had put the recovered data to the iMac
11. from the iMac, poke around the external drive and move the desired files and folders to the iMac
12. done
The only reason I tried DW before DR III was because I already had DW on the MBP, from the last time I'd worked with a bad disk (and DW had succeeded).
In your case -- if you don't have access to another Mac on which to run either recovery program -- you'll have to change out the iMac disk and get a fresh copy of whatever system you're using there on it, and only then drop the bad disk in an enclosure, connect it to the iMac, and get to work.