Well, personally I'm fond of the OA samurai but a core rules samurai is not hard at all. Just play a straight single class fighter and RP the code.
Requried feats: (Greater) weapon focus, (Greater) weapon spec, Improved Crit. All for the bastard sword. Power attack is required as well. Try to sweet talk your DM into letting keen and improved crit stack and focus on milking 2:1 PA and critical damage for all it's worth. Combat Expertise is optional but highly recomended. Exotic Weapon Prof [bastard sword] is completly optional, most of the time you should be wielding your sword two-handed anyway for the power attack. Wear the heaviest armor you can find and carry a longbow and spear as your backup. Put skill ranks in intimidate, ride and jump. Assign your stats as follows: Str then Dex then Con but don't forget to put a 13 in Int if you intend to take Expertise. There, that is your basic samurai, the rest is just a matter of focus.
Other important feats:
Iorn Will (cuz you don't want to fail a fear save and have to comit sepuku in disgrace

)
Cleave, Combat Reflexes and maybe Imp Sunder. For the "wade into the horde and build a bulwark out of their corpses" samurai.
The mounted archery chain, if it looks like you will be spending any time in the wide open spaces at all.
The spring attack chain. If you decide you want to go the lightly-armored samurai route.
Improved init, Quick draw and one level of Rog. For the iaijutsu master (don't forget to also charge and PA your flat-footed opponents in the first round in addition to the sneak attack). Improved Disarm can be his backup trick on round 2+. Combines well with the spring attack samurai.
Also consider multiclassing for 2 levels of monk. That 2 level dip nets you a +3 to all your saves, improved unarmed strike, two bonus feats which complement the samurai style nicely, evasion, and a few skill points to blow on balance or tumble or diplomacy or spot or listen all for the cost of one point of BAB and a few HP. The only real problem with this is that it slows down your all-important aquisition of Greater weapon focus/spec.
So at third level I would build a samurai somthing like this.
Human
Str 15 Dex 14 Con 12 Int 13 Wis 10 Cha 8
Feats: Iron Will, Power Attack, Weapon Focus [bastard sword], Cleave, Combat Expertise
Hope that helps.