Quick RAM question

Hi, i have a quick question i wanted to ask. I have a Dell Dimension B110, with a 2.5GHz processor. I use DDR PC3200 RAM, and currently have 2 RAM slloots in my computer (both taken by 256MB RAM) for a total of 512 MB. My computer teacher in school currently bought alot of RAM for the school computers in his class, and asked me if i wanted to trade both my 256 for one 1GB RAM. I know that 1 GB is more than i currently have, but i also heard that for best performance, you should use memory in pairs of 2 of the same. So, is 1 1GB better to have in my comp, or would 2 256MB have better performance? Thanks in advance for the help.