The problem is many American depts are wary of international students that don't have a strong command of English, especially one that has problems in other areas. And the only way you'll really be able to convince them is with at least a good GRE score... Your GRE verbal is alarmingly low, while a department might just gloss over it if you are an American student, since you are international they will automatically suspect that you don't speak English well (and yes, even American students that speak English fluently sometimes get low verbal scores!).
As to getting your score up quick, a score of 320 makes me suspect you have problems with the test overall... The GRE verbal doesn't just test vocabulary, although it is a major component, especially with the antonyms section. Before you start memorizing words, pick up a GRE study aid and read the 'how to take the test' section carefully. You probably will be able to increase scores in other areas, such as reading comprehension, without having to do lots of memorization... You just need to know the correct way to approach the test.