Can I set up Airport express with Motorola sb5100 or do I need a wireless router?

[purvih]

I'm sorry if this is a stupid question but I have been trying to set up my newly acquired airport express to work with my Macbook with little luck. I have a Motorola cable modem (SB5100) provided by Virgin Media and my airport express has never moved beyond the flashing amber yellow stage despite having followed the instrcution manual perfectly. I am very new to mac and have never set up a wireless network before so am wondering what it is I am doing wrong. Someone please guide me through this. Do I need a router in addition to the modem? Isn't Airport express supposed to be that router? Thats what I thought when I bought it but when I called Apple support they told me that I did not have the right wireless router!