Instalation and kernel headers

I am trying to install Virtualbox, and after several times with the same error, I try to check all the steps of the installation in depth, and I see this message

First Installation: checking all kernels...
Building only for 2.6.32-5-amd64
Building initial module for 2.6.32-5-amd64

Then I check my kernel, and I see that (aparently) my installation has the 64 bits architecture

$ uname -a
Linux linuxpc 2.6.32-5-amd64 #1 SMP Sat May 5 03:03:41 UTC 2012 x86_64 GNU/Linux

But I am pretty sure I installed the 32 bits version. In fact, if I revise the /etc/apt/sources.list file, I have this line

deb cdrom:[Debian GNU/Linux 6.0.4 _Squeeze_ - Official i386 DVD Binary-1 20120128-12:53]/ squeeze contrib main

For sure, I tried to install the 64 bits version of Virtualbox, and I got an error because the wrong architecture.
And, of course, my question is: what's happen? I have a 32 or 64 bits installation?

NOTE: To install Virtualbox, I follow the steps described in, Squeeze Backports

Best regards.



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