I think I may be able to help you.
My problem was in two places. I suspect yours is the same. I kept getting the error in iTunes due to an error with Windows Update. Whenever I tried to install updates for Windows, it would start and NEVER finish. I checked the update log and discovered (by right clicking on files and viewing the details) that the error code was 8007000B. After a BUNCH of digging around for a fix for this error I found one that worked.
Here's what you do:
1. Delete iTunes and Quicktime. (Yes, again. lol)
2. Visit the link below and follow the instructions.
http://windowshelp.microsoft.com/Windows/en-US/Help/ca7d15d7-8ee3-4993-bd01-753d adc904121033.mspx
3. Be sure to press the enter key after you type in the string they tell you on that page. You will see a confirmation that the action was successful.
4. Restart your computer and then install iTunes in the normal fashion. Just double click the install file and let it run.
This should help. If it doesn't, I don't know what to tell you. Mine worked perfectly after doing this.