How to remap brightness & volume keys on Asus AspireOne / Ubuntu Lucid?

Question

I want to remap the following keys on my Asus AspireOne running Ubuntu Lucid:

Brightness down (Fn-Left)  -> Home
Brightness up   (Fn-Right) -> End
Volume up       (Fn-Up)    -> Page up
Volume down     (Fn-Down)  -> Page down

xmodmap -pke says this (only relevant lines shown):

keycode 232 = XF86MonBrightnessDown NoSymbol XF86MonBrightnessDown
keycode 233 = XF86MonBrightnessUp NoSymbol XF86MonBrightnessUp
keycode 123 = XF86AudioRaiseVolume NoSymbol XF86AudioRaiseVolume
keycode 122 = XF86AudioLowerVolume NoSymbol XF86AudioLowerVolume

So I entered the following:

xmodmap -e "keycode 232 = Home"
xmodmap -e "keycode 233 = End"
xmodmap -e "keycode 123 = Prior"
xmodmap -e "keycode 122 = Next"

This has no effect on the stalwart brightness keys, which keep on brightening. The volume keys at least have the decency to stop changing the volume, but now do nothing.

What else can I try to achieve the desired result?

---

Edit - output of xev

xev seems unhelpful. For any press or release of any of the buttons I get something like this:

FocusOut event, serial 30, synthetic NO, window 0x6e00001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event, serial 30, synthetic NO, window 0x6e00001,
    mode NotifyUngrab, detail NotifyAncestor

KeymapNotify event, serial 30, synthetic NO, window 0x0,
    keys:  0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0
           0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   0

Where the serial number increases on every key event and first digit of the keys array is either 0, 1, 2, or 8, though the choice seems sort of random.

I'm guessing this is bad.