My name is Sanjeev and I am from Dell.
Please visit the Dell support site by clicking the link below to find the graphic card which is compatible with your Inspiron 531shttp://accessories.us.dell.com/sna/category.aspx?c=us&category_id=6715&cs=19&l=en&s=dhs&mfgpid=192780
Are you serious? Get advertising out of this forum. $150 for HD 6450 is a ripoff!
@OP: I'd suggest getting something like HD 6670 low profile:http://www.newegg.com/Product/Product.aspx?Item=N82E16814102958