One important note here: If you use a normal analog TV which most portable TV are you will not read the text on the screen very well at all.
I'm not sure of the exact reason but I have hooked a computer to a small analog TV and you can not read the text very well if at all.
Something about those TVs just makes them unsuitable as a computer monitor.
You can share one monitor with the help of a KVM switch though.
A KVM switch is a device you hook your monitor, keyboard and mouse into and all of your computers also and it has a button to switch between the two computers.
Edit: From a quick search, it appears part of the reason analog TVs don't work that well is the resolution is limited to 640x480.
Edit 2: From a quick search, it appears if you have a PS2 keyboard and mouse with a VGA monitor you can get a KVM Switch for about $25.