What was old money and what was new money? New money in "The Great Gatsby" was money that people were making illegally and old money in "The Great Gatsby" was money that people were making the old fashion way. In "The Great Gatsby" Gatsby was making new money. He was selling illegal alcohol and making a lot of money because of it. He was making money the new way. Gatsby was getting money quick and this was making him rich fast. By him getting quick money he was allowed to throw elaborate parties, have a nice house, have nice cars, and have anything he wanted. Money was not a problem for Gatbsy. Whenever he needed money; he got it.
However, Tom was getting money the old fashioned way. Tom was making old money. He was a good citizen and he obeyed the law. He got his money from his job and he didn't get his money by doing anything illegal. All of his money was earned legally. Tom didn't know what Gatsby's job was, but he guessed since Gatsby got rich fast, had elaborate parties, a nice house and a nice car, that he was doing something illegal. Tom thought that Gatsby was a bootlegger and that he was selling illegal alcohol. (http://www.fa-mag.com/component/content/article/687.html?issue=32&magazineID=1&Itemid=73)