Can you tell me something about the perfomence of those two differnt
CPU´s ?

There's very little difference, but if you pay for a software product and
tell suppoprt "I'm using an AMD processor" and they only support intel
then
the automatic answer is going to be "**** you; we don't care; don't
call us again unless you're running intel."

Check with your software vender. Or at the very least, don't tell them
if you run AMD and they don't support it.

What vendor have you had this experience with?

How much difference *can* there be? It's not hard to test a CPU and find
out whether it faithfully implements the specified instruction set.
Debugging a CPU is much easier than, for instance, debugging a medium-sized
computer program, because there is only a small set of things it has to
do -- a few hundred things -- all of them very well-defined.

What software actually has problems with AMD vs. Pentium? I'm curious.