it is highly unlikely that you have a 64bit OS on that system. The only 64bit server systems sold by dell are the 7150 , 3250 and 7250.
I believe you are asking how to check if you are using the ia32e (x86_64) and taking advantage of the 64bit-extensions that are available on these processors. 'uname -a' should return x86_64 in the line. the xeon are still 32bit cpu but have 64bit extensions
running
Code:
for i in `rpm -qa | grep kernel`; do rpm -q --qf %{arch} $i && echo " " $i; done
will return anything with kernel in the line in the form of 'arch rpmname'
the kernel you are running should be ia32e
hope this helps