How can I reinstall Windows 7 if I lost my installation DVD? [duplicate]

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.

Windows 7 RTM

• 32-bit Windows 7 Home Premium
• 64-bit Windows 7 Home Premium
• 32-bit Windows 7 Professional
• 64-bit Windows 7 Professional

Windows 7 SP1

• 32-bit Windows 7 Home Premium
• 64-bit Windows 7 Home Premium
• 32-bit Windows 7 Professional
• 64-bit Windows 7 Professional
• 32-bit Windows 7 Ultimate
• 64-bit Windows 7 Ultimate

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.

Windows 7 RTM

• 32-bit Windows 7 Home Premium => CC9D8220B2179E784D85BF1EA98D2EE2190D534F
• 64-bit Windows 7 Home Premium => 336779EA6B65F63E11A609B4D021439C47AB315B
• 32-bit Windows 7 Professional => 697FA06554502FB21D30275273B25747299C020D
• 64-bit Windows 7 Professional => 50127304441A793EE51B3F501289F6599A559E9F

Windows 7 SP1

• 32-bit Windows 7 Home Premium => 6071B4553FCF0EA53D589A846B5AE76743DD68FC
• 64-bit Windows 7 Home Premium => 6C9058389C1E2E5122B7C933275F963EDF1C07B9
• 32-bit Windows 7 Professional => D89937DF3A9BC2EC1A1486195FD308CD3DADE928
• 64-bit Windows 7 Professional => 0BCFC54019EA175B1EE51F6D2B207A3D14DD2B58