SMP problems in Dual Xeon with 2.4.25 and 2.6.5

Hi everybody. 

I have a Dell Poweredge 1600SC (2 Xeons 2.40GHz) with problems running
kernels (2.4.* and 2.6.*) with SMP with or without hiperthreading. 

The machine is only 100% stable when I run a kernel without SMP (nosmp).
With kernels 2.4.* I get signals 8/11 doing kernel compilation. With
2.4.25 I get the segmentation fault in gcc only in one of 400
compilations (but sometimes with more frequency and sometimes with less
frequency). 

I have test my hardware with some dell diagnostic tools, with memtest86
for long without detect any problem. I have the BIOS firmware, the RAID
firmware, and the processors microcode up to date.

With 2.6.5 I get ocasional compiler errors compiling the kernel (2
errors after 200 compilations), for instance:
  xfs_bmap.c:5194: internal compiler error: in expand_stmt, at   
  c-semantics.c:869
  Please submit a full bug report,
  with preprocessed source if appropriate.
  See <URL:http://gcc.gnu.org/bugs.html> for instructions.

and also sometimes I see strange ^@^@^@^@ chars in the files generated
during the compilation (which fails). For instance, one line in my
mm/.depend:

   /usr/src/linux-2.4.25-test/ð^]^@^@ude/linux/bootmem.h \

I have tried different kernel parameters (noapic apm=off acpi=off) but
without success with smp (with or without hyperthreading).

My configs:
http://213.97.99.199/otros/config2.6.5
http://213.97.99.199/otros/config2.4.25

I'm using debian, but also happens with other distros.

Any idea? Now, I my mind is blank ... It's this the correct forum to ask
this question?

Any help will be appreciated.

TIA,

Vicente