Fn key doen not work on compaq presario laptop in Xubuntu feisty

I own a Compaq Presario V3228AU laptop with an AMD Turion 64bit processor, running Xubuntu Feisty, with an onborad Nvidia geForce6150 display card, 512MB RAM. I have installed the latest Nvidia driver from the repositories. The Fn key is not supported. It does generate an ACPI event that is referred to 'X' but there is no action. Only the Fn+F7 (brightness down) and Fn+F8 (brightness up) key-combos are trapped; the other functions (lock,sleep,web,print,play/pause, stop, next, prev) are not accepted. However, despite this there is no change in brightness ot the screen. I have a dual boot with Windows XP, and the keys work fine there. Here's the output from dmidecode:
$ sudo dmidecode -s system-manufacturer
Hewlett-Packard
$ sudo dmidecode -s system-product-name
Presario V3000 (RZ819PA#ACJ)
$ sudo dmidecode -s system-version
F.21

The output from ACPI is as follows:
$ sudo tail -f /var/log/acpid
[Mon Jun 11 17:13:21 2007] starting up
[Mon Jun 11 17:13:21 2007] 55 rules loaded
[Mon Jun 11 17:13:23 2007] client connected from 4667[107:114]
[Mon Jun 11 17:13:23 2007] 1 client rule loaded
[Mon Jun 11 17:13:25 2007] client connected from 4759[0:0]
[Mon Jun 11 17:13:25 2007] 1 client rule loaded
[Mon Jun 11 17:17:10 2007] completed event "video LCD 00000087 00000000" ///// Fn+F7 --br. down
[Mon Jun 11 17:18:06 2007] received event "video LCD 00000087 00000000"
[Mon Jun 11 17:18:06 2007] notifying client 4667[107:114] ////hald-addon-acpi:
[Mon Jun 11 17:18:06 2007] notifying client 4759[0:0] //// 'X'
[Mon Jun 11 17:18:06 2007] completed event "video LCD 00000087 00000000"
[Mon Jun 11 17:18:09 2007] received event "video LCD 00000086 00000000" ////// Fn+F8 -- br. up
[Mon Jun 11 17:18:09 2007] notifying client 4667[107:114]
[Mon Jun 11 17:18:09 2007] notifying client 4759[0:0]
[Mon Jun 11 17:18:09 2007] completed event "video LCD 00000086 00000000"

I had filed a bug in a similar thread for Kubuntu, but was recently told that this problem is specific to Xubuntu, and that Feisty-Kubuntu was doing the job fine. Is there a way to modify the existing Asus/Thinkpad/Sony brightness scripts for my purpose? (these are already installed)