on BSD, there is no handling of the horizontal component of a scrollball input.
The following patch adds this handling for the WSMOUSE and USBMOUSE parts of the
mouse driver so that with eg the Apple Mighty Mouse the scrollwheel works in
both directions.

Index: xorg/xserver/xorg/hw/xfree86/os-support/bsd/bsd_mouse.c
===================================================================
RCS file: /cvsroot/xsrc/xorg/xserver/xorg/hw/xfree86/os-support/bsd/bsd_mouse.c,v
retrieving revision 1.1.1.1
diff -u -r1.1.1.1 bsd_mouse.c
--- xorg/xserver/xorg/hw/xfree86/os-support/bsd/bsd_mouse.c	15 Mar 2006
17:13:34 -0000	1.1.1.1
+++ xorg/xserver/xorg/hw/xfree86/os-support/bsd/bsd_mouse.c	6 Nov 2006 20:31:39
-0000
@@ -56,12 +56,15 @@
 
 #define HUP_GENERIC_DESKTOP     0x0001
 #define HUP_BUTTON              0x0009
+#define HUP_CONSUMER		0x000c
 
 #define HUG_X                   0x0030
 #define HUG_Y                   0x0031
 #define HUG_Z                   0x0032
 #define HUG_WHEEL               0x0038
 
+#define HUC_AC_PAN		0x0238
+
 #define HID_USAGE2(p,u) (((p) << 16) | u)
 
 /* The UMS mices have middle button as number 3 */
@@ -431,6 +434,11 @@
 	    dz = event->value;
 	    break;
 #endif
+#ifdef WSCONS_EVENT_MOUSE_DELTA_W
+	case WSCONS_EVENT_MOUSE_DELTA_W:
+	    dw = event->value;
+	    break;
+#endif
 	default:
 	    xf86Msg(X_WARNING, "%s: bad wsmouse event type=%d\n", pInfo->name,
 		    event->type);
@@ -492,6 +500,7 @@
     hid_item_t loc_x;		/* x locator item */
     hid_item_t loc_y;		/* y locator item */
     hid_item_t loc_z;		/* z (wheel) locator item */
+    hid_item_t loc_w;		/* w (pan) locator item */
     hid_item_t loc_btn[MSE_MAXBUTTONS]; /* buttons locator items */
    unsigned char *buffer;
 } UsbMseRec, *UsbMsePtr;
@@ -611,6 +620,7 @@
     dx = hid_get_data(pBuf, &pUsbMse->loc_x);
     dy = hid_get_data(pBuf, &pUsbMse->loc_y);
     dz = hid_get_data(pBuf, &pUsbMse->loc_z);
+    dw = hid_get_data(pBuf, &pUsbMse->loc_w);
 
     buttons = 0;
     for (n = 0; n < pMse->buttons; n++) {
@@ -702,6 +712,9 @@
     if (hid_locate(reportDesc, HID_USAGE2(HUP_GENERIC_DESKTOP, HUG_WHEEL),
 		   hid_input, &pUsbMse->loc_z, pUsbMse->iid) < 0) {
     }
+    if (hid_locate(reportDesc, HID_USAGE2(HUP_CONSUMER, HUC_AC_PAN),
+		   hid_input, &pUsbMse->loc_w, pUsbMse->iid) < 0) {
+    }
 #else
     if (hid_locate(reportDesc, HID_USAGE2(HUP_GENERIC_DESKTOP, HUG_X),
 		   hid_input, &pUsbMse->loc_x) < 0) {
@@ -714,6 +727,9 @@
     if (hid_locate(reportDesc, HID_USAGE2(HUP_GENERIC_DESKTOP, HUG_WHEEL),
 		   hid_input, &pUsbMse->loc_z) < 0) {
     }
+    if (hid_locate(reportDesc, HID_USAGE2(HUP_CONSUMER, HUC_AC_PAN),
+		   hid_input, &pUsbMse->loc_w) < 0) {
+    }
 #endif
     /* Probe for number of buttons */
     for (i = 1; i <= MSE_MAXBUTTONS; i++) {