Different builds exist based on the capacities/age of the processor (CPU) on the machine the browser build is to be launched; if your CPU is archaic and doesn't support the SSE instructions set, use the -ia32 variant (sometimes referred to as "-nosse"); if your CPU is somewhat newer and does support SSE (but not SSE2), use the -sse variant; if your CPU does support SSE2 (and later), then you should use the "normal" build, whose filename ends in just "-xpmod.7z"...
PS: Not relevant for XP users, but if you're on Win7+ x64 OS and want to use roytam1's NM28_x64 fork (you may have your reasons ), there's a fourth (64-bit, only) build variant that's meant for CPUs supporting AVX2 ; filename ending in "-w7plus-avx2.7z"...
So, now you know ...