i have had similar issues with multiple operating systems, and it sounds like there might be a problem with your actual dvd rom drive. some of the older drives will have issues, but i cannot be sure this is your problem. either way i know for a fact that UltraISO Premium works well in Windows 7, you can use this program to mount the image or if your download was like mine you should get all the files of the 7048 install disc in a folder and should just be able to click and run the setup.exe file without burning or mounting any image. but REMEMBER a 64 bit OS can not start the installation from within a 32 bit OS. You will need to run the setup.exe file from within a 64 bit Windows OS or burn the files to a disc and boot from the disc.
Hope this helps some,
sceadwe