Windows XP SP3 (Legal) download?

I have my CD-key sticker with me but don't have the CD anymore. Is there anywhere I can download Windows XP SP3 installation disc from?

If you have a sticker that is on the side of a computer, it is an OEM licence and only valid for the machine it came with. Contact your system builder who should be able to order you a new one for a minimal charge + shipping.

If you have a fully packaged product and can not find the CD, contact Microsoft, who again for a minimal charge + shipping should be able to order you a new media kit. Alternatively, if you have a MSDN or Technet Subscription, you may get lucky (but not always) and download a version from there and using your serial key.

Microsoft provides a Windows XP SP3 download for virtualization:

Windows XP Mode

Windows XP Mode for Windows 7 makes it easy to install and run many of your productivity programs that run on Windows XP directly from a computer that runs Windows 7.

Windows XP Mode provides a 32-bit virtual Windows XP Professional Service Pack 3 (SP3) environment. This download includes a virtual hard disk (.vhd file) with Windows XP SP3 preinstalled. Client virtualization software, such as Windows Virtual PC is required to use Windows XP Mode.

https://www.microsoft.com/en-gb/download/details.aspx?id=8002

The "Windows XP Mode for Windows 7" download will give you a WindowsXPMode_en-us.exe file.

To isolate the virtual hard disk, use an archiver app such as Keka. Right-click any .exe file and Open With to extract it.

1. Download WindowsXPMode_en-us.exe, extract to WindowsXPMode_en-us
2. In the sources folder, rename xpm to xpm.exe and extract it.
3. In the resulting new xpm folder, find the VirtualXPVHD file.
4. Rename VirtualXPVHD to VirtualXP.VHD by inserting a period before the file extension.

VirtualXP.VHD is the Virtual Hard Disk that can be loaded by a Virtual Machine.