unknown hard error...

Hi everybody

I am having a big problem installing Windows XP on an Intel Imac.
I downloaded the latest version of Parallels desktop, the 4.0.3810 from the official site, as a trial and I installed on my machine, that has a LEopard X 10.5.6 as OS.
the installation seems to work fine, I found no problem on doing that. I opened the program, to install Win and I followed the tutorial for the virtual machine: I selected the type of OS, than I choose tipical installation, the name of the partition and the shared folder options. Than I clicked the start button on the top left of the window for installing Windows. I choose express, than I typed the Win product key.... and here begin problems.
I have to choose where is the new OS. I insert the cd into the drive... and LEopard show me an icon of an empty cd. I tried inserting the cd again, after cleaning it with a towel but the cd is read as empty. (it's the original copy)
I made a copy of the disk using a windows pc... same result.
I thought that it could be a hardware problem, but at the moment I cannot replace or fix it, so I tried to go on and install Windows from an .iso image.
again, with the Windows pc I made an .iso... using nero and a convertor software (nrg2iso). this time the installation seems to go on. I see a bios-like screen and then the blue screen of the Windows installation. on the bottom part of the screen, it shows the files that are loaded, but it freezes on "starting windows..." (I don't know what is the exact phrase because my OS is in italian). Then I have another blue screen with just two lines:
STOP: c00002221 Unknonw Hard Error
\SystemRoot\System32\ntdll.dll

At first I thought: wrong iso. I did something wrong.
I made another one, with boot files, nothing
I tried another software (easyiso)... same result.

I am goingo to try Parallels Transporter, with my pc, but I'm not very convinced with this option. I tried also yesterday and it was veeeeeeery slow, and the process stopped nearly at 40%.

Have you some suggestions to this matter? there is something else that I could try??
please, any help would be very appreciated, I relly don't know what to do.
I know that the Windows cd is right. I have re-installed it on my pc a couple of months ago and it worked fine
Any help? please??