AutoCAD 2000 was designed for the hardware of its era. It requires a processor and Windows 2000 , making it incredibly lightweight by today's standards. For a "portable" setup, this means the entire program and any files can easily fit on a small, inexpensive USB flash drive, ready to run on a wide range of older or low-powered computers.
Yes, there is. While Autodesk does not make such old versions available for general download, there are legitimate pathways for existing customers and students. autocad 2000 portable link
If you are attempting to run legally purchased legacy software on modern hardware, the recommended technical solution is to use Virtualization (such as VirtualBox or VMware Player). You can install a compatible older operating system (like Windows XP) within the virtual machine to run AutoCAD 2000 safely and legally using your original license key. AutoCAD 2000 was designed for the hardware of its era