xav1er

If your laptop has DP, you just need to buy DisplayPort<->DisplayPort cable or DisplayPort<->MiniDisplayPort cable (don't know if your laptop has DP or miniDP - both possible). I'm using miniDP<->DP converter and then DP<->DP cable.

normal DP output looks like this (similar to HDMI but slightly different): http://www.startech.com/media/ProductPhotos/SV231DPDDUA_DisplayPort_Connector_Comparison.jpg

miniDP looks like this: http://upload.wikimedia.org/wikipedia/commons/4/47/Mini_DisplayPort_on_Apple_MacBook.jpg

pretty sure that you can order these cables from amazon or ebay

This problem is because HDMI standards; resolution 2560×1600 is supported by HDMI 1.3 or higher. make sure your laptop's HDMI port is version 1.3 or higher and you have a proper HDMI cable that can supports HDMI 1.3 top resolution.

I've got similar problem with my 30" dell (2560×1600p) but I'm playing on PC (much more convenient way for playing poker for me), my graphic card has both HDMI and DisplayPort outputs - I'm using DisplayPort now and it works just fine, but I guess your laptop does not have a DisplayPort output. Thats why buyin this "display cable" wont work for you imho. You need to have DisplayPort output om your laptop and most laptops dont have these.

http://en.wikipedia.org/wiki/HDMI#Version_comparison

You may also try this:

http://www.notebookcheck.net/2560x1440-or-2560x1600-via-HDMI.92840.0.html