22. The system of claim 18 being further operable to: detect an occurrence of a first cursor event at the first client system, wherein the detection of the first cursor event includes detecting a location of a cursor at the first display being positioned over a portion of displayed content representing the first specific portion of modified web page content; and cause the first client system to automatically display, in response to detection of the first cursor event, a first pop-up window or layer which includes a first portion of advertising content that is different from the first specific portion of text.
22. The system of claim 18 being further operable to: detect an occurrence of a first cursor event at the first client system, wherein the detection of the first cursor event includes detecting a location of a cursor at the first display being positioned over a portion of displayed content representing the first specific portion of modified web page content; and cause the first client system to automatically display, in response to detection of the first cursor event, a first pop-up window or layer which includes a first portion of advertising content that is different from the first specific portion of text. 24. The system of claim 22 being further operable to: identify at least one category associated with the first web page; causing a first client system to automatically display a first pop-up window or layer which includes selected advertising content; and wherein the displayed first portion of advertising content is contextually related to the at least one identified category associated with the first web page.