can someone explain the difference between standard previews and 1:1? you can have lightroom batch prepare either within a folder, so you don't have to spend time looking at the "working" notice when toggling between pictures in loop view. but i don't understand the difference between these. What i really want, is to have lightroom batch prepare thumbnails at the size I want, and previews of the size I want, for all files within a folder. then I can review quickly. Unfortunately, the thumbnails appear to create themselves ONLY when i have paged to them in grid view. and the 1:1 batch takes forever, for 300+ RAW files (12 megapixel). I have a dual core XP box with 2 gig of ram...

See Ian Lyons' posting #26 in the Adobe Lr forum:
go here.

Just keep in mind there are two sizes of previews being discussed here. One you have control over size-wise but you're still better off speed wise going 1:1. But your library size will get a lot larger.