How do I restore my O/S file from a Macrium Image?

[ImnoGuru]

Hello and thank you for looking at my thread today.

I recently had a problem with my main computer not being able to to updates of any kind.
During a clean out of potential viruses with SuperDave @ Computerhope here (Thanks SuperDave) it was discovered that the problem is actually my Windows Installer has been corrupted.

My Dell is running Windows XP Pro SP3 (legal) however I dont have the original install disk. 

To my good fortune (I hope) I also had reason to get Macrium Reflect from this thread and take an image of my computers C: drive, onto an external drive. 

My discussions with various people tell me that I might be able to replace the corrupted files with the image from the external drive.

To do this I need to connect the external drive to the computer and follow the instructions from the Macrium website, but how do I find or select the actual file that is damaged?
Can I just select that file, or do I need to just replace everything indiscriminately.

Your guidance would be greatly received.
Thank you ImnoGuru.

[ImnoGuru]

Ok, here's a glitch in the whole restore senario. 

I dont have Macrium installed on the hard drive and the Windows Installer (which is the corrupted file) wont let me install Macrium Reflect.

Any ideads as to how I might go about this then?

[Computer_Commando]

http://www.microsoft.com/downloads/en/details.aspx?FamilyID=5a58b56f-60b6-4412-95b9-54d056d6f9f4&displaylang=en

[ImnoGuru]

Thanks Computer_Commando.
I went there. Read through it all and selected my link.

Unfortunately that did not fix it.

I also tried the firewall, (PC Tools) just in case there was a block on a site that I needed for the updates. I set everything in the list to allow. I open Firefox as usual to go to all my sites and still I dont get anything in the way of updates, even Adobe installs fail.

I've rebooted and tried again but still no joy.

My Windows Security Center will not change. Automatic updates is OFF and will not change. Doesnt matter where I try to change it. (Control Panel Desktop in the actual window, so on).

As for the Macrium Image.. I cant get that to work either, as the program keeps giving me a message reading "Unable to find the specified path".
Macrium, it seems, allocates a Drive letter for the recovery but I always get the same message, using their suggestion or even if I try to change it to another location.. eg" desktop "G" "F" or anything through to "Z".

My name it seems is most apt at this point. hahaha.
ImnoGuru.