I have an Inspiron 537s and I want a new ATI card, but are there any (other than ATI Radeon HD 4350, because I ordered that with my computer) that are in the Slim size?
Yes, that is a low-profile ready card (will fit your slimline). What you need to do with that card is remove the pre-installed (full-size) metal bracket and replace it with the two included low-profile brackets (see them in the fourth image). Very easy to do, btw.