Can I use my Windows 7 CD to install Windows 7 on my other computer?
Solution 1:
The DVD can be used on other computers, even from different manufactures, but you need to have a valid key for that second computer.
Solution 2:
KCotreau is right, but it may be worth adding...
For OEM Windows versions, that key is generally on a sticker stuck on the computer somewhere. The sticker is kinda your proof of ownership of a legal copy of Windows. E.g. if some pirate manages to generate your key and get it activated using a keygen, you'll probably need to show the sticker as proof that you're not the pirate. Thankfully, I've never had this happen (I think the usual pirate trick is to bypass activation etc, so the licence key isn't needed at all).
For the same basic kind of Windows (e.g. "Windows 7 Home Premium"), you can re-use the disk on another computer, so long as you have a key for that machine - the disk isn't specific to the key. The same version but with a different service pack will also work. A different version (e.g. trying to use Windows 7 Home Premium with a Windows 7 Home Basic serial) will not work - at the very least, expect Microsoft to start demanding you pay for an upgrade when you go online.
Even with OEM Windows (though it's against the terms), you can generally get away with transferring a license from one machine to another. Wipe it from the old machine, then install it on the new. Just don't try to use it on both at once. Basically, Microsoft can't really tell the difference between "new computer" and "replaced dead motherboard, had to replace lots of other bits to be compatible with the new one". Expect to have to do phone activation and declare that the license key is only installed on one machine, though - internet activation often fails for this (even for non-OEM Windows where you have the right to move it from machine to machine anyway).