Install On Dell Inspiron 1525

I'm trying to do a clean installation of Windows 7 x86 on my Dell Inspiron 1525 laptop that I bought in July 2008. It's been running Windows Vista 32-bit without any trouble. Yesterday I purchased the Windows 7 Professional 32-bit upgrade from Digital River and downloaded the ISO. I've burned it onto two separate DVDs using different software and a different computer each time (the second time I used Alcohol 120% and made sure that it was on the slowest setting). Now I'm downloading the iso again.

Each time I try to install it (which has been many times, now, trying different configurations of partitions, etc) I get the error message "Windows cannot install required files. The file may be corrupt or missing. Make sure all files required for installation are available, and restart the installation. Error code: 0x80070570"

I've read through just about every thread I could find on this site and others and nothing seems to help. The only thing I haven't done is mess with the RAM, but I'd prefer not to do that as I don't have any experience opening up laptops (although I have built three desktops).

Anyone have any ideas/suggestions?