RPG hittesting!

im having a little trouble with hittesting… i have made an RPG where you move around a character with arrow keys, but im having trouble making him stop when he walks into a wall.

this is the code i have for the character:

onClipEvent (enterFrame) {
if (Key.isDown(Key.RIGHT)) {
_root.Character.gotoAndStop(4);
} else if (Key.isDown(Key.LEFT)) {
_root.Character.gotoAndStop(3);
} else if (Key.isDown(Key.UP)) {
_root.Character.gotoAndStop(2);
} else if (Key.isDown(Key.DOWN)) {
_root.Character.gotoAndStop(11);
}
}
onClipEvent (keyUp) {
if (Key.getCode() == Key.DOWN) {
_root.Character.gotoAndStop(1);
} else if (Key.getCode() == Key.UP) {
_root.Character.gotoAndStop(12);
} else if (Key.getCode() == Key.LEFT) {
_root.Character.gotoAndStop(13);
} else if (Key.getCode() == Key.RIGHT) {
_root.Character.gotoAndStop(14);
}
}

and this is the code im using for the background:

onClipEvent (load) {
movespeed = 8;
}
onClipEvent (enterFrame) {
if (Key.isDown(Key.RIGHT)) {
_x-= movespeed;
}
else if (Key.isDown(Key.LEFT)) { 
_x+= movespeed;
}
else if (Key.isDown(Key.UP)) { 
_y+= movespeed;
}
else if (Key.isDown(Key.DOWN)) { 
_y-= movespeed;
}
}

Yh its a game where the background moves around the guy and he always stays in the middle of the screen.

In the background i have a movieclip called walls. and i need some help with the code to make the background stop moving when the character hits the wall.

Thanks for all the help you guys have given me recently.