Karlosp.net

1. Download aircrack-10b2madwifi-r3366ar5007
2. Open a console with CTRL+ALT+T
3. Execute: sudo bash
4. Execute: cd / ; tar vfxz /home/user/aircrack.tgz [make sure to do from /]
5. Execute: modprobe -r ath_pci wlan_scan_sta wlan
6. Execute: mv /lib/modules/2.6.21.4-eeepc/atheros ~ [move old stuff to home directory as backup]
7. Execute: depmod -a
8. Execute: modprobe ath_pci

A quick HOWTO:
airmon-ng stop ath0
airmon-ng start wifi0
aireplay-ng -9 ath0

You can download my auto web crack bash script.
auto-wep-crack
Within script replace 00-15-AF-78-F0-59 with your MAC address!

Source: http://scottn.us/2008/03/asus-eee-pc-with-aircrack-ng.html