The KVR667D2N5 is not listed on the Kingston compatibility list for the Dimension E520.
www.kingston.com lists the two 800MHz CL5 Module below
4 x KTD-DM8400C/1G $46 each at Kingston
2 x KTD-DM8400C/2G $86 each at Kingston
Welcome to brand name computers using special memory.
However, if you can find out which MOBO is in the Dell, you might find other modules that might fit.
Search the web for better prices