Access to a PC NAS HDD from a Mac

Hi all, 2 days ago I made the leap from PC to MAC (new imac) after 15 years a PC user, thanks to a positive experience with a 3G iphone. I am still learning with baby steps about the MAC world.

Problem:
I have connected my PC NAS HDD directly to my Airport Extreme Base Station (ethernet cable). My other PC machine connected to the airport wireless network can read/write to the NAS HDD, but my IMAC (wireless connection) does not see it. I have tried looking for it by IP Address with the prefix of both smp://<ip address> and ntf://<ip address> but no joy.
Is there any way I can map the the HDD or my other PCs to be visible on my MAC?

I assume something similiar to this has been discussed already so if you can point me in the right direction, I would greatly appreciate it.

Thanks

Does that network drive you are using require any special drivers to be installed? One I used to use did.

That aside, file sharing between Windows and OS X is simple.
File sharing between Mac and PC