[G4] airport question

[Margaret Krakowiak]

I live in 1/2 of a duplex, I rent out the other half.
I'd like to provide my tenant with internet access.
She has a laptop with an airport card, currently goes
to the coffeeshop to connect.
I have a Quicksilver tower, and use a DSL modem.

I have never had a need for wireless with my setup.
I say this because I've been trying to research/figure out
what I would need to get, and I'm not clear.
Do I need an airport card?
Do I need a wireless router?
Do I need a base station?