Does a 2.4GHz & 5GHz router require a special wifi card?

I bought a D-LINK Dir-855 , http://www.dlink.com/products/?pid=548, works great.

But it is not clear to me if, when I switch on both the 2.4Ghz wifi network and the 5 Ghz network, how I should use it on my laptop?

I can only use one wifi network at the same time? Do I need some special kind of wifi network card? (I have an old ibm t-60 notebook).

I'm a little confused here, if the user bought a nice dual band 802.11n router with a lot of bells and whistles, why wouldnt he want to get the most out of it, rather than staying on the built in G/N capabilities of his old Toshiba.

Yes, the router uses 2.4 and 5ghz simultaneous bands,
Yes, that creates two simultaneous streams, but
No, not all N cards or adapters can run off of and take advantage of both the 2.4 and 5ghz dual band routers out there.

You will need to get a new dual band adapter or PCI slot card to connect to both bands, and you decide which channel, channel width, and wireless mode from your router configuration.

IPCONFIG/ALL from your CMD prompt and then open up a browser and type in your Default gateway to access your router. Usually 192.168.1.100 or something like that. Understand that your distance goes down with 5ghz, but you get a cleaner band to play on.

Ask yourself, is it worth the money to get all of these components or is N at 2.4ghz good enough?

This is not technically an answer to the question asked, but a clarification to counter some of the misinformation here. The frequency of the signal (2.4 vs 5 GHZ) and the wifi standard (802.11 B vs G vs N) are two different things. While you are more likely to find 5 GHZ and 802.11N together because both are more recent capabilities of later model routers, those same routers are generally capable also of broadcasting 802.11 B/G, and 802.11N can run at either 2.4 or 5 GHZ (or both on a dual-band router).