Airport Express +IPad2with WiFi + Windows XPvia cable modem

[gottago]

I have just bought the iPad2 with WiFi only.........bought in the US along with the Airport Express base Station (recommended by the Apple Store)
At home I have Windows XP operating thru a cablemodem.

I cannot get it all hooked up so they will operate together ( the pc in one room & the ipad in another?

Do I need to buy something else or am I doing something wrong?

If by some chance I don't need the Airport express base station can I get a refund even tho purchased in the US & we live in Aust?

Thanks