Question : Problem: Do I need AIRPORT EXTREME BASE (SIM DUALBAND)-GBR

I am new to Apple and have recently bought an iMac. I already have a couple of Windows PCs in my home and a D-Link Wireless Router. I would like to be able to have wireless network in my home so that I can wirelessly access files on one computer's (Apple or Windows based) from another computer. I am not able to do that at present. I have also bought Apple's AIRPORT EXTREME BASE, though I have not yet opened the packet yet.
I would appreciate if somebody could advise me whether I need to have and AIRPORT EXTREME BASE or not in the presence of my D-Link Wireless Router. Basically I wish to understand what is the difference between the wireless router that I currently have and the AIRPORT EXTREME BASE that I have bought. What it is that AIRPORT EXTREME BASE can do for me that a Wireless Router can not do. Lastly I also wish to know whether I would be able to connect AIRPORT EXTREME BASE to my wireless router or not.    

Answer : Problem: Do I need AIRPORT EXTREME BASE (SIM DUALBAND)-GBR

The Mac should be able to connect to any wireless router. The DLink should work fine. You do not need the Airport Extreme.

The Airport Extreme is basically a Mac branded wireless router.

Since it is newer than your DLink, it is possible that it may support a faster protocol. For instance the new Airports will support both Wireless G and Wireless N simutaneously. Depending on how old your DLink is, it might be the older Wireless B, or the newer WIreless G. Unless you bought it in the last couple of years, it is not likely the fastest wireless N.