Can anyone tell me if it "generally" true that a laptop can drive say a projector or external screen at a higher resolution than its internal screen, or are they "generally" limited to the internal screen res? I know this might be an "it depends" answer, but the external max resolution is not always specified. I will want to drive 1920x1080 or 1400x1050 from a laptop that will probably have a 1366x768 screen. Also, am I likely to have distortion if the external aspect ratio doesn't match the internal screen, or does this depend on the graphic chip and something I need to look into carefully before buying? Thanks.
It depends on the graphics chip (IGP/dedicated). Generally speaking, resolutions on an external screen are limited by the external screen resolution, the interface used & graphics chip.
A laptop screen with 1366x768 resolution doesn't mean having an external screen connected to it will also be limited to the laptop screen resolution.
No, you aren't likely to have any distortion.
What you call “internal resolution” is the native resolution; that is, the resolution that maps correctly to the LCD screen (1 pixel of resolution to 1 physical pixel on the screen). Any distortion, smearing, etc. is caused by the display trying to map a non-native resolution to something it can display. CRTs don’t have native resolutions and are generally able to scale any resolution up to their maximum without problem.
When you connect an external monitor, if it is an LCD or projector, it too will have a native resolution and may be different from that of the built-in display. If it is a CRT, then it won’t have a native resolution, and it should be able to display anything up to its maximum.
Also, when you connect an external display to a laptop, you get multiple displays in the Display Properties dialog (assuming Windows™) and should be able to set the resolution for it independently from the internal display. So when you do connect one, just set it to whatever resolution you want if it’s a CRT or if it’s an LCD, to the native resolution of that display (not the internal one).
That said, if you want to use a really high resolution, you will need to make sure that your laptop’s graphics chip can support it, though most video adapters from the past decade or so can support at least up to 1600, even in laptops. Pretty much any projector under $1,000 will be limited to either 800x600 or 1024x768, so that won’t be an issue because your laptop will almost positively be able to do that. However if you intend to connect a monitor, you’ll want to confirm that your display adapter can support the resolution you will use (the res you want for CRT or need for an LCD).
It should be easy enough to find out what resolutions your display adapter supports by checking the Display Adapters branch of the Device Manager to identify your graphics chipset then Googling for its name + maximum resolution.