It is the same machine. It has a 2.66 GHz processor, 1 GB of RAM right now (I
had 512 mb, upgraded to 1.5 GB three years ago, then the 512 GB burned out and
now I have 1 GB left).
The problem happens only in Ubuntu's Gnome, especially when the effort done
by the computer is huge, especially with a lot of folders open, a lot of
pictures open, the browser open with several websites, Open Office Writer loaded
with a 100 mb file or larger, Picasa filled like a sponge with tens of thousands
of pictures.

root@aptosidbox:/home/alexzmeurarul# 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 : 2659.647
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 sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe lm
constant_tsc up pebs bts pni dtes64 monitor ds_cpl tm2 cid cx16 xtpr
bogomips : 5319.29
clflush size : 64
cache_alignment : 128
address sizes : 36 bits physical, 48 bits virtual
power management:

root@aptosidbox:/home/alexzmeurarul#

Is there any problem with my CPU ?