Did a quick test with another XP system, also this system could't connect. Seems the only system that can connect with my config is the windows 7 system.
Tonight I will do some wireless sniffing to see what's the difference between Windows 7 and XP connecting. Starting my OpenVPN tests now.
Can I suggest the following:
1)
Install the crda package to get the country regulatory stuff actually applied.
2)
For your configuration
config 'wifi-device' 'wlan0'
option 'type' 'mac80211'
option 'country' 'NL'
option 'hwmode' '11bg' (or maybe better: option 'hwmode_11n' 'g')
option 'channel' '5'
option 'disabled' '0'
config 'wifi-iface'
option 'device' 'wlan0'
option 'network' 'lan'
option 'mode' 'ap'
option 'ssid' 'XXXXXXX'
option 'hidden' '0'
option 'key' 'XXXXXXXX' (and make sure this HEXA only key has more than 8 digits)