What resolutions are you running the monitors at? It may be that you are running them both at the same resolution - in which case the 14" could only be showing part of the screen as it supports a lower maximum resolution (you should be able to scroll around the full desktop with the mouse if that is the case).
How do you have them set up at the moment? Showing one big desktop (stretched) or both showing the same thing (cloned)?
Opteron firstname.lastname@example.orgGHz (stock HS/fan), Asus A8N-SLI SE (passive NB), 1.5GB RAM (2:3:2:5, 2T), WD Raptor 740GD 74GB, Maxtor DM10 300GB, Asus EN7600GT SILENT@???, M-Audio Revo 7.1, Nebula DigiTV, Dell 2005FPW, Enermax 431W Active.