Cannot set screen resolution to 1400x1050 on laptop

[paulfielding]

I'm running Virtualbox on my Windows XP host. The native resolution of the machine is 1400x1050. However, after installing Guest Additions for either XP or Windows 7 (the two OSes I've tried installing), The largest resolution I can select is 1152x864. I'd like to be able to go full screen at 1400x1050.

Am I missing something?

Paul