Other players can't connect to my SRCDS.

[ReVolut1on]

Hello there!

Server OS: Windows XP Pro 32bit
Processor: Intel P4 3.2Ghz HT ON
Ram: 2GB
Game(s): Counter-Strike: Source
Start Up Command: C:\srcds\orangebox\srcds.exe -console -game cstrike -tickrate 100 +map cs_office -maxplayers 16 -autoupdate
Admin Mods: SourceMod

Bandwidth: 8M/1M
Router: Bewan iBox v1.0
Local server IP: 192.168.100.26
External IP: 88.113.230.239

We're trying to set a CS:S dedicated server on my friend's house. The server-PC is connected to the router LAN1-port and all other computers in the house use wlan. We use an old P4 PC with XP (clean install) and installed the server via hldsupdatetool per the instructions in here. Everything seemed to go flawlessly. I've disabled the Windows firewall and no other firewalls/antivir programs exist.
We joined the server via other comp that is connected via WLAN to the network. Then we invited another guy from somewhere else and gave him the IPs. He couldn't connect, for some reason. We tried to give him both local and external IPs but no success. We noticed that this server comp has the exact same external ip than the another comp that we use for playing cs. Could this be a problem and if it is, what can we do to correct it? Neither of us are experienced in networking business so we are pretty much clueless.
We'd greatly appreciate any help!

Thanks!

[BjornR1989]

You must forward the port that your server is running on (most likely 27015 both TCP and UDP) from the WAN port on your router to your internal server IP.
In essence you're telling the router "If a packet arrives from the outside on this port, send it to that local server on the same port".

Do not, i repeat: do NOT connect via a wireless network.
A wireless network is half duplex and only one client can send or receive a packet at a time, causing huge lags.