It depends. If the Lakers as a team play their A game, the Spurs don't really have much of a chance even if they play their A game. If the Lakers play their B game, Spurs could definitely win the series if they play their A game. Basically, if you were to assume that the Spurs and Lakers play their best, IMO the Lakers would come out on top every time. As was quite evident in Round 1 against the Twolves, the Lakers are somewhat inconsistent, and IMO they probably won't be able to play four straight A games against the Spurs, which is why I'm predicting they'll lose at least one game, if not two or three (or four if the Spurs play well enough and the Lakers play only average).
To be specific, Fisher and George must play well, like they did in Round 1 (thank god Fox is injured!). Horry must also play decently (don't be surprised if he makes important shots 😉). So if Fisher, George and Horry play well and Kobe and Shaq play their usual ball, I can't see Parker, Duncan, Robinson, Rose, Ginobili, Jackson or anyone else being able to stop them. Horry is really going to have to step up his D on Duncan, though I think Horry did just fine against KG in Round 1. Today's Game 6 was a bit of a preview as to how the Lakers will handle Duncan in the post; that is, a Laker is going to have to effectively double Duncan with Horry like they did with KG today (though nobody can really stop KG).
Prediction: Lakers win series 4-1.