Normally you'll want to set HS_OSC for any crystal frequency over 4MHz. Some 4MHz
crystals may work with the higher drive levels, some won't.

With HS_OSC OSC2 provides a higher drive level to the crystal. With XT it's lower. The
lower drive level with your 10MHz crystal was most likely not providing enough for the
crystal to start up.

Here's an excellent set of basic PIC training modules: http://techtrain.microchip.com/x14/

Download & go through the one on oscillators.

adcon1=7 is essentially the same as ADCON1 = 1110 right?
Nope. ADCON1 = 7 is the same as ADCON1 = %00000111, which makes all analog pins
digital.

ADCON1 = %00001110 is the same as ADCON1 = 14, which leaves AN0 set to analog, and
the rest digital.