Effective weight training for female swimmers-Y/N?

I've joined an online 'milage club'-a group of people with various abilities,some training for marathons others coming back from injuries,all keeping track of and sharing their efforts-and the topic of weight training has come up.Out of 30 or so people I am the only one who swims as well as biking/walking,everybody else runs,walks,bikes or does the elyptical.Does weight training differ for swimmers vs. runners?I swim ***/back stroke only-no free-and I feel as if I already do a lot of upperbody and if I add weights as they are suggested in this blog-I'm gonna compromise my ablity to swim eficiently.Any thoughts or ideas? blog.metaboliceffect.com/.../