Your swimming speed is more confined by your skill level. You can be the world's strongest man/woman and get your ass handed to you by a 130lb kid with a little training in speed swimming. I would say if you want to get faster in the pool, you're better off just staying in the pool and swimming.

That said, if you just want to weight train because its healthy and you want to be stronger then great! I really don't think you stand to gain much as an endurance style athelete by weight training though. If you were a sprinter, the yes of course.

Just my 2 cents.

IronWorker