There used to be Windows XP virtual machines on modern.ie. I still have a couple of copies around for testing. Unfortunately after XP going out of support, they were removed. But the copies used to be on Azure CDN (credit /u/JoshBrodieNZ. Seems like they recently removed them too.

There's still a way to get Windows XP 32-bit VMs from Microsoft (no 64-bit) through Windows XP mode. It contains a VHD (virtual hard disk) with a 32-bit Windows XP SP3.

EDIT 2022-01-12: The link below is dead. Looks like Windows XP Mode was tied to Windows 7 and removed when it went EOL.

1. Download Microsoft XP Mode from https://www.microsoft.com/en-us/download/details.aspx?id=8002.
2. Using 7-zip or any other utility decompress the exe.
3. Inside sources, there's another file called xpm. Decompress it too. With 7-zip, right click on it and select "Extract to ... ."
4. One of the extracted files is VirtualXPVHD and around 1.2 GB. Rename it to VirtualXP.vhd.
5. In VirtualBox (or any other virtualization software that supports importing VHDs), create a new Windows XP 32-bit VM and use this file as the hard disk. When you start the VM, it will start a Windows XP setup. My mouse did not work, but you can use shortcut keys to navigate the installer (e.g. Alt+N for Next).
6. ???
7. Profit.

For a step by step guide with pictures, check this post from howtogeek.com.