question about powershot a610

im gonna get the camera in the end of the month, but i wanna purchase the memory card in advance from ebay. can u tell me if it is ok to put a 2 gb sd card and what should be the minimum speed of it? i wanna record movies with the highest quality and i dont want any skipped frames. should i go with 120x, 133x or 150x? and if u can tell me briefly if there are significant differences between the quality of the movies/pictures of the a610 and a620, since 620 is only with 20 euro more expensive