Hi,
Please see this FAQ:
http://www.displaylink.com/support/ticket.php?id=329
You can drive 2560x1440 over DP or HDMI.
Note that HDMI can only drive 2560x1440@50Hz.
2560x1440 over DVI-D is not supported.
Cheapest option would be a USB-DP or USB-HDMI adapter.
Thanks,
James