Two things to note.
1) Multiclassing two classes that have important class-based progression (ie. Challenge and Spellcasting) is more detrimental than beneficial because you are constrained by action economy. You only have a standard and move or a full-round each turn regardless of how many options for action you have available to you (barring certain explicit exceptions).
2) You're going to be stretched thin getting all the ability scores to back up your abilities. Str for melee, Dex for defense, Con for HP and Fort Saves, Cha for casting. You'll end up being sub-par in all categories.
So, since you don't want to tank Wis since everyone needs perception and will saves, your only real option is Int. Then, it comes down to which are you going to favor. I strongly, strongly suggest, that if you're going to do this, you do not go for a 50/50 split. I'd say no closer than 25/75 so you'll want to end up with either a Sorc 5/Samurai 15 or a Sorc 15/Samurai 5. So it's really a matter of which do you want more, casting or martial. Next, of course, is the matter of action economy. For this, you can take a page from the Reach Cleric's book. The Reach Cleric uses his standard action for spellcasting and wields a Reach weapon (ie. Longspear) with Combat Reflexes to make his melee attacks as AoOs. You could easily pull this off using a Naginata. If you're going to rely on touch spells (melee or ranged), then you won't need Cha quite as much since you don't need to worry about high DCs.
Another option, if you don't mind dropping the spellcasting, is Eldritch Heritage. That gets you the Bloodline Powers. Then you could be an Abyssal, Orc, Shadow, whatever heritage that meshes well with a martial class (Samurai in this case). Lastly is the prospect of Gestalt class; a set of houserules in which you take full progression in two separate classes. So at lvl 1, in your case, you'd be a Samurai 1/Sorc 1. At lvl 2, you'd be a Samurai 2/Sorc 2, so on and so forth. You take the best BAB, Saves, Skill Points, HP etc. between the two classes (so BAB and Fort Save from Samurai, Will save from Sorc, and roll both their hit dice and take the higher result). It tends to be a bit unbalancing, especially if there are other non-gestalt characters so most GMs won't really go for it unless it's a whole Gestalt campaign. You also suffer more from action economy, again because broader options are constrained by the same standard/move|full-round limitations.
So what, exactly, are you looking for? A Martial who supplements with spellcasting? A Caster who is a little more competent at melee?
