Dell Latitude XT VGA D-Sub external monitor max resolution

Hi there, I'm planning to purchase a new LCD Monitor to attach it to my Dell Latitude XT via de VGA (D-SUB HD-15) connector and I'm wondering which is the maximum recommended resolution for the grafic card an ATI Radeon Xpress 1250, so I can purchase the monitor that better suits this resolution in order to avoid distortion, lack o details etc.

Thanks in advance