32 bit or 64 bit?

I have a Dell Inspiron 531.It has an AMD Athlon 64 X2, Dual-Core 4400+ processor. I think that qualifies it as a 64 bit processor? But when I download the Nod32 v 3 64 bit installation file, it tells me that my processor does not support this. So then I download the 32 bit installation file and it works fine. What's going on here? Am I just as well protected with the 32 bit file. I seem to remember that in v 2.7 it didn't matter which file you used. Confused.
Oh -other than that v 3 seems to be working fine on all three of my computers--All Dell - one is WinXp Home, one is WinXp Pro, and this one is Vista.

 

you must have also 64-bit vista

 

You need the 32 bit versions . You may have x64 processor but the OS is obviously 32 bit variant . Yes , the 32 bit protects you

 

Thanks for the quick response.