James Van Der Beek will guest star on an upcoming episode of 'Law & Order: CI.'

According to TVLine, the 'Dawson's Creek' veteran will play Rex Tamlyn, described as an "overconfident, hard-partying playboy." The character is a partner in a Facebook-esque website that's devoted to hooking people up for fleeting romantic trysts.

Like 'The Social Network,' there's a lawsuit around the idea of the site, but with this case there are a few murders mixed in. It's 'Criminal Intent,' what do you expect? Thad and Trent Luckinbill also guest star.

Van Der Beek will appear in the ABC midseason comedy 'Apartment 23' as a fictionalized version of himself.

In other casting news ...

• Martin Short and Aidan Quinn will guest star on Showtime's 'Weeds.' Short will play an attorney and Quinn has been tapped to play the CEO of an investment firm. Other guest stars include Jennifer Jason Leigh, Lindsay Sloane, Pablo Schreiber, David Clennon and Gary Anthony Williams. [Showtime]