Is it possible to do two 3way switched circuits that share a common power source but the power source and the light wire are in the same box?
Yes, 

You need 14-3 or 12-3 going to each switch from the light/power:

Call the switches L(eft) and R(ight):

Connections@Light:


LineInPwr(white) -> Lamp(white)  
LineInPwr(black) -> L(white tagged black)
LineInPwr(gnd) -> tied in common Both L(gnd) and R(gnd)
L(black) -> R(black) [traveler]
L(red) -> R(red) [traveler]
R(white tagged black) -> Lamp(black)


Connections at L switch:


L(White tagged black) -> L SW (common)
L(Black) -> L SW (brass) [traveler]
L(Red) ->  L SW (brass) [traveler]
L(gnd) -> L SW (gnd)


Connections at R switch:


R(White tagged black) -> R SW (common)
R(Black) -> R SW (brass) [traveler]
R(Red) -> R SW (brass) [traveler]
R(gnd) -> R SW (gnd)


Our own BMitch provided an answer and diagrams here (originally found here). We differ slightly in wire assignments (mine's better ;-)(why? both switches have the same wire assignments, the magic happens at the light)), but its basically the same.