Help with wireless on Macbook

[seshomaru samma]

My friend has a macbook - the latest model. Lately she can't connect to the wireless router in our office. I was called to solve the problem , but have no clue how to go about it. It looks like a lot of the Bash commands don't work on a mac. Like : iwconfig , ifconfig eth1 up ( i realise it names the connections different like en1 or something), iwlist eth1 scanning , dhclient etc...
If I click on the 'airport' icon I can see our router listed , when I choose it nothing happens. Sometimes it connects ,sometimes not.
I tried restarting the router and the computer.
Any advice?

[Alfa989]

What's the router's brand?

[seshomaru samma]

the router is
TP-LINK (chinese)

does it matter?

EDIT: A windows laptop can connect to it !
I connected the macbook with a cable to the router but the situation is still the same :
the status is 'connected', we get all the bars in that gui thing (don't know how to call it) ,but safari still cannot connect.
I need to add that it has a WEP key.
I set it up with a Debian laptop . It was working perfectly with both the Debian and the Mac until last week.
I might bring my laptop in tomorrow to check it out , but I'm interested in how to solve it on the Mac