You can go to Sourceforge, find the project page for UFO:AI, go to the SVN online browser, and for the trunk click on "Download Tarball" or something - I forget off-hand exactly what it says - but with that option you can directly download the whole trunk in a compressed, packaged file.
I'd recommend 7zip to un-compress it, as the standard built-in .zip decompression of Windows won't handle it, and WinZIP is quite frankly bloated crap compared to 7zip and other alternatives. (Although to be fair, I haven't tried any recent version of WinZIP to review it, I've refused to touch it for some time...)
With this method you don't need Tortoise SVN or any other special program to get the SVN trunk copy, except the utility I just mentioned to decompress it.
The downside is that you can't use this method to update automatically, you have to download the whole big thing all over again to get an updated copy.