Heh, I quickly figured it out. Okay, here we go.
Step 1 : Make sure DosBox is running
Step 2 : Press Ctrl+F1 to Start the Keymapper
Step 3 : Looking at the Keymapper, you should be able to find where the extended keyboard is located.
Step 4 : Click on "8", three buttons should appear below "Select an event to change"
Step 5 : Click on "Del". This removes the key event attached to that key aka pressing it will no longer type out the number 8.
Step 6 : Click on "Add" and press the Up key on your keyboard. Now when you press the 8 on your extended keyboard, Dosbox sends a "Up key-down" event. So Num-lock doesn't matter now

Step 7 : Repeat Steps 4-6 to assign 7->Home, 9->PgUp, 4->Left, 6->Right, 1->End, 2->Down, 3->PgDn.
Now if you forgot to delete a previous key event.... Scenario: You forgot to remove the normal event for extended keyboard key "6" but added in the event for the right arrow.
Step 1 - Click on "6"
Step 2 - Near the bottom-left of the keymapper are: Event:key_kp_6 and Bind:
Step 3 - Click on Next (if needed) so that the line with Bind on it says: "Bind: Key [6]"
Step 4 - Click on "Del". Now it should say: "Bind: Key right"
Hope this post helps ^_^