ivan,
Excuse me for butting in but what is the difference between the i686 to pentium4 versions of any DLL and why is there the two versions?
The packages are built with CPU specific optimizations, and those will differ between i686 and P4. In particular for the P4 CPUs the focus is on using the MMX, SSE and SSE2 instruction set.
Keep in mind that this whole approach is applicable to multiple GCC compilation options, be it '-mtune' or '-march', and there are always the more generic options that just focus on generating either FASTER code, or SMALLER code.