Possible Duplicate:
Where do I download Windows 7 (legally from Microsoft)?
I have lost my Windows 7 installation DVD, but I do have the license key. How can I get a Windows 7 DVD? Can I download an ISO image somewhere? While installing can I use my original Windows 7 Key?
UPDATE: Sadly someone at Microsoft has discovered this back door in to their ISO library and plugged it, The links to the ISOs no longer function. I am leaving this question up for historical purposes.
Digital river is the distribution company Microsoft uses for it's digital downloads. This site has aggregated a list of the files they use for when distributing downloads (here for SP1). I have used it before and but not recently, however the links should still be good. Your license key will work as long as you download the same edition (Home Premium/Professional/Ultimate) as your key corresponds to. The architecture (64-bit vs. 32-bit) and language do not matter with activation.
To help verify that your downloads of the Digital River ISOs are good, below are the SHA-1 hashes for the ISOs, copied from Microsoft TechNet. Each link is a permalink to the corresponding TechNet page from which I got the hash. I've personally downloaded all the ISOs and verified the hashes.
As described in this Microsoft KB article, if it is a retail copy, you have the following recourse:
To request replacement hardware or software, contact the Microsoft Supplemental Parts team at the appropriate contact number that is provided in the "Contact Information" section. You must be in possession of the product (if it is damaged or defective) and be able to provide proof of purchase. The customer service representative will advise you of any replacement costs or shipping and handling fees that may be charged. If a product is no longer under warranty, the replacement item may no longer be available.
If it is an OEM copy, then they advise you to contact your OEM for the replacement disc instead.
