I have had the opposite experience as EMG--my newts are fully aquatic, rarely on the land area. I originally had mine in a 10G but now they are in a 20G long. I'm looking at a 2.5G I have set-up and it looks a little small for a newt, although with careful planning I think it could work. If that's all you have to work with, I'd set up some type of platform so the water can go all the way across to provide a larger amount of water. This will help give the newt more swimming area (if s/he wants it) and help with water quality. It would also give two distinct levels and increase your "floor space" like a loft. I'm not sure what you could use with such a small tank for filtration, you might have to do every other day water changes. If you only have a half tank of water, it's not really enough space for an ADF--they like to sort of "jump" from top to bottom, and that doesn't leave a lot of swimming room. A firebelly toad would work much better in my opinion--mine is pretty lazy although he occasionally swims back and forth to check out the view. Truth be told, 2G is really not enough room for much, your best bet would be to hold one betta in a full tank of water. Other more "interesting" animals that would be OK in that small a tank are a couple of shrimp. I have a couple of endler's and a couple of shrimp in a planted 2.5G and it looks pretty good.
10G tanks are cheap, what, about $10? I'd spring for it and a decent filter (I use a Fluval 1+) and scrounge around for some rock you might already have, steal a few plants from another tank, and set it up pretty cheaply. You can always upgrade later, in fact, if you do 2-3 times water changes weekly you could forego the filter until you could afford one--they are messy. Mine will only eat frozen bloodworms, one will occasionally touch newt bites if I don't feed bloodworms, the other goes on a hunger strike until the bloodworms are produced.
Good luck, there are a lot of people who do "nano tanks" and they have done some pretty amazing things.
Jackie