At the bare minimum, you should be able to count to ten and know common pleasantries. Just attempting to communicate in the local dialect can go a long way towards making friends with strangers. This shows a willingness to learn the culture and communicate on the terms of the locals.
Both of our Spanish skills have gotten pretty rusty over the years so we bought the entire Rosetta Stone to practice. It's not cheap, but you are able to download it to two computers so we only used one download, and let our mechanic use the second download in exchange for occasional help and advice.