hang on here, xp does have the potential to run faster than win 7 in various cases, e.g. say u have a 10 yr old computer, xp will run much faster on it than win7, and even if you bought a new comp today, xp would probably out perform win7 because its an older OS, which requires less powerful hardware to run. its like putting win 95 on one of today's comps, sure it will run fast, but it wont have many features...However XP is not that basic, it does everything most people want it to do...esp if ur a gamer, most games still come out as DX 9 because most people have decided to stay on XP. XP still has a lot of support behind it, and it doesn't look like that support is dropping anytime soon.
Win 7 is NOT the best OS that's come out, think of it as a replacement for vista, while MS make a win 8 that's completely different... So far XP has been the most succesful OS for MS. If u want sheer speed go with xp, xp still has many great features. Win 7 may have muti-threading and all that, but it will drain and use more hardware resources in order to run, ur choice. i think XP even supports dual cores and all that. get like a 64 bit xp pro version. or a win 7 home 64 bit - make sure ur lappy is 64 bit compat, (basically if its new it will be 64 bit).