I'm sure you know the a 300 dpi 11x17 has more pixels and take up more ram/ diskspace than one @ 144 dpi. both are 11x17. more often than not it's not recomended to enlarge. shrink and enlarge back, the main reason is that photoshop will "interpelate" - guess image iformation, I'm impressed with the different bi-cubic re-sampling options available is CS, but, in the end it's inventing detail that is not there. if you paint / render a 11x17 image, on any thing smaler than a 11x17 canvas and enlarge, prepare for less detail. if your low on memory see if exit-ing all other programs, helps I think there are options in PS concerning memory, I think you can also adjust how much, PS is dedicating it's self in the preferences.