PowerISO is a utility which in short is to either create data disks or extract data from disks.. I've never actually used it so I'll outline two possible ways of using it..
1. If you place the disk in your drive, then start PowerISO and click extract. It will then ask where and what needs extracting, this is where you point it to your D drive (or whichever letter denotes your disk drive). I'm sure if you clicked on Help which is usually located at the top right hand side of the PowerISO box it'll give you guidelines on how to proceed.
The website has a FAQ and on extraction it says:
Q: How to open ISO file and extract files from it?
A: Because of its file associations, you can open an ISO file by simply double click on it. After open the ISO file, click "Extract" button
2.You may be able to 'drag and drop' the file into PowerISO. Start up PowerISO then put your disk in the drive then whatever is contained on the disk hold your mouse cursor over it and hold down the left mouse button, you will now find that you can move this around as long as you don't release the mouse button. You want to then 'drag' the object over to the open window of PowerISO and let go of the button. It should now just a question of clicking extract, although you will probably be asked 'where' you want it extracted to.. Just choose your documents or something like that. I hope this doesn't sound too convoluted and you can understand it ok..Good luck