64bits upgrade

I have just discovered to my surprise that my home machine is 64 bits capable.

cat /proc/cpuinfo
processor    : 0
vendor_id    : GenuineIntel
cpu family    : 15
model        : 4
model name    : Intel(R) Celeron(R) CPU 2.66GHz
stepping    : 9
cpu MHz        : 2660.159
cache size    : 256 KB
fdiv_bug    : no
hlt_bug        : no
f00f_bug    : no
coma_bug    : no
fpu        : yes
fpu_exception    : yes
cpuid level    : 5
wp        : yes
flags        : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc up pebs bts pni dtes64 monitor ds_cpl tm2 cid cx16 xtpr lahf_lm
bogomips    : 5320.31
clflush size    : 64

So the logical step would be to upgrade to a 64bits OS. 10.04 or OpenSolaris?