Follow all previous advice.
A half gallon is a horrible thing for even shrimp to live in.
You could also go to walmart and look for the 2 gallon Heritage Hill jar from Mainstay. =] it looks like this:
It only cost me $9.50. =] It's a great temporary home till you can buy the Aquaculture 5 or 10 gallon Kit from Walmart! =] Look in your fish section! =] They cost about $30 and $40 respectively. =] add the price of a marineland heater at $30 (Petsmart, or online for like $17), Gravel at around $5, water conditioner at around $5, a gravel vac for $5 (a nice small one is at Petsmart I reccomend a smaller one. =]), and food at around $3. you've only got to spend around $100 dollars up front for a fish.
After that though it's only about $10 dollars a month with electric, water, and food to keep taking care of it. =]
It cost a LOT more up front and long term to care for a dog/cat/furry or reptillian friend. =/
Or you could just get a big clear storage container permanently though it would be harder to enjoy your fish as it wouldn't be as easy to see them. =/
You could also just get the jar in the picture, an adjustable heater(I suggest marineland's 25 watt stealth heater or the 25 watt hydor theo) , and a penplax small world filter http://www.petco.com/product/3199/Pe...ld-Filter.aspx
. It's on sale for $5 and other users here recommend it if I remember correctly. in fact at this price I may just buy one. =]
If you're going to buy a real tank though I HIGHLY recommend buying one from PetCo now what with their dollar per gallon AND 4th of July sale. =] That is if you live near one. I unfortunately live nowhere near one. =[
Get em while the gettin's good! =]