When I'm faced with a statement like 'If you're absolutely sure you want to delete them, then....' it makes me wonder whether I'm doing the right thing. Problem is, I don't actually know what they do and what happens if I do delete them. FYI, they are on a second hard drive which I used to use with XP - and it was the only HDD on the machine then. I installed a second HDD and put W7 on it and now use the original HDD for back up. It has some residual folders which I want to get rid of - these SIDs (if I'm using the right terminolog) are some of them, Users is another and Documents and Settings another. Please tell me whether I'm likely to wish I hadn't if I delete them, or whether in the circumstances I describe they have no importance.