I don't see that AutoCAD runs on Linux, it says Windoze and Macs.
It appears that some people do get AutoCAD to run on Linux using WINE, a Windoze emulator, but that looks like a messy business, so I'd look into it carefully before spending money. It does appear that older versions of AutoCad like you have work fine, from what I read, but I'd want to be sure for the specific configuration I intend to buy and install.
Dual boot with Linux is not tricky, just install Windoze first, then install Ubuntu and it can re-partition your disk, install Linux, and set up the dual boot for you. Then you edit the Windoze boot list so it asks you if you want Linux or Windoze when you boot, and when Windoze clobbers the boot record with it's own stuff, you can still get into Linux easily. I can tell you how to do all that, in as much detail as you care to put up with.
Whether or not you can run Linux is entirely a matter of hardware support, so unless your machine has obscure or fancy bleeding edge hardware, everything should work fine, except printing which sometimes lacks functionality available on Windoze and is slower. Of course, as with any new operating system, some learning is required, but Ubuntu works hard to be easy.
My advice would be to do one of these:
1.) Stick with Windoze.
2.) Dual boot, getting a bit of help if you need it.
3.) Find somebody that runs AutoCAD on Linux (there are forums, etc.) and get help in setting up AutoCAD under WINE on Ubuntu.
I'd do #2 or #1. I would not blame you a bit in the circumstances for sticking with Windoze.