How do i ping/see computers on a vpn whereas the openvpn logs tells me I am connected?

I explain my situation, I am running ubuntu with openvpn
OpenVPN 2.1_rc11 i486-pc-linux-gnu [SSL] [LZO2] [EPOLL] [PKCS11] built on Oct 15 2008
and the log tells that i am right connected apparently, see below:
Thu Mar 19 11:53:07 2009 us=456716 Current Parameter Settings:
Thu Mar 19 11:53:07 2009 us=456835 config = 'gso.ovpn'
Thu Mar 19 11:53:07 2009 us=456866 mode = 0
Thu Mar 19 11:53:07 2009 us=456894 persist_config = DISABLED
Thu Mar 19 11:53:07 2009 us=456923 persist_mode = 1
Thu Mar 19 11:53:07 2009 us=456951 show_ciphers = DISABLED
Thu Mar 19 11:53:07 2009 us=456979 show_digests = DISABLED
Thu Mar 19 11:53:07 2009 us=457006 show_engines = DISABLED
Thu Mar 19 11:53:07 2009 us=457037 genkey = DISABLED
Thu Mar 19 11:53:07 2009 us=457064 key_pass_file = '[UNDEF]'
Thu Mar 19 11:53:07 2009 us=457091 NOTE: --mute triggered...
Thu Mar 19 11:53:07 2009 us=457143 246 variation(s) on previous 10 message(s) suppressed by --mute
Thu Mar 19 11:53:07 2009 us=457178 OpenVPN 2.1_rc11 i486-pc-linux-gnu [SSL] [LZO2] [EPOLL] [PKCS11] built on Oct 15 2008
Thu Mar 19 11:53:07 2009 us=457347 /usr/sbin/openvpn-vulnkey -q gsokey
Thu Mar 19 11:53:07 2009 us=684384 WARNING: file 'gsokey' is group or others accessible
Thu Mar 19 11:53:07 2009 us=684556 Static Encrypt: Cipher 'BF-CBC' initialized with 128 bit key
Thu Mar 19 11:53:07 2009 us=684606 Static Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication
Thu Mar 19 11:53:07 2009 us=684695 Static Decrypt: Cipher 'BF-CBC' initialized with 128 bit key
Thu Mar 19 11:53:07 2009 us=684727 Static Decrypt: Using 160 bit message hash 'SHA1' for HMAC authentication
Thu Mar 19 11:53:07 2009 us=684782 LZO compression initialized
Thu Mar 19 11:53:07 2009 us=768281 TUN/TAP device tap0 opened
Thu Mar 19 11:53:07 2009 us=768353 TUN/TAP TX queue length set to 100
Thu Mar 19 11:53:07 2009 us=768440 /sbin/ifconfig tap0 10.3.0.8 netmask 255.255.255.0 mtu 1500 broadcast 10.3.0.255
Thu Mar 19 11:53:07 2009 us=773597 Data Channel MTU parms [ L:1577 D:1450 EF:45 EB:135 ET:32 EL:0 AF:3/1 ]
Thu Mar 19 11:53:07 2009 us=773721 Local Options String: 'V4,dev-type tap,link-mtu 1577,tun-mtu 1532,proto UDPv4,ifconfig 10.3.0.0 255.255.255.0,comp-lzo,cipher BF-CBC,auth SHA1,keysize 128,secret'
Thu Mar 19 11:53:07 2009 us=773754 Expected Remote Options String: 'V4,dev-type tap,link-mtu 1577,tun-mtu 1532,proto UDPv4,ifconfig 10.3.0.0 255.255.255.0,comp-lzo,cipher BF-CBC,auth SHA1,keysize 128,secret'
Thu Mar 19 11:53:07 2009 us=773823 Local Options hash (VER=V4): 'e08453d7'
Thu Mar 19 11:53:07 2009 us=773873 Expected Remote Options hash (VER=V4): 'e08453d7'
Thu Mar 19 11:53:07 2009 us=773934 Socket Buffers: R=[112640->131072] S=[112640->131072]
Thu Mar 19 11:53:07 2009 us=773970 UDPv4 link local (bound): [undef]:5028
Thu Mar 19 11:53:07 2009 us=774002 UDPv4 link remote: 82.125.157.213:5028
Thu Mar 19 11:53:08 2009 us=317446 Peer Connection Initiated with 82.125.157.213:5028
Thu Mar 19 11:53:09 2009 us=40549 Initialization Sequence Completed
Thu Mar 19 11:53:17 2009 us=169057 WARNING: 'ifconfig' is present in local config but missing in remote config, local='ifconfig 10.3.0.0 255.255.255.0'

But when i try to ping/see others computer in the virtual networks i can ping
10.3.0.10 the openvpn server located in another subnet 255.255.255.0
10.3.0.9 an other virtual client located in the same subnet of mine.

I cannot see another clients that there are not in my subnet. I mean I can't see other virtual clients in another subnet. For that i use nmap -sP command with
192.168.0.0/24 see only 'real' clients in my subnet
10.3.0.0/24 see only 'virtual' clients in my subnet

And finnaly like other case, when i'm running windows with openvpn, the log is the same but I can see other virtual clients. In conclusion it works normally on Windows but not under Ubuntu.