Just for the aftermath some info: according to a tool reading the
CPUID of my processor I do have an AMD Athlon XP 2000+ at 1666 MHz which has the features SSE, SSE FP, SSE MX, MMX, MMX+, 3DNow!, 3DNow!+, CMOV and MTRR. Please note that there is nothing like SSE2 or so in the list.
Fact is that with all SSE optimizations turned off SFML is on the "safe side" aka "less troubles" aka "beginner friendly".
On the other hand it scares me a bit that enabling an optimization of the compiler produces code which causes horrific behaviour on processors not having the features necessary for said optimization. Is it common like that? Is there no "fall back path" during runtime in case the feature is missing? is the behavior really that horrific (crashes without any hint on what went wrong)?