PC2700 ram in an ECS mobo that takes only PC2100

hey just wanted to know if this could be done with out any problems arising .. thanks

You are fine. You can always put higher rated ram into your motherboard which is specified for lower rated ram. You can also bump up the fsb higher to make your ram work harder. But if you have an ecs k7s5a board I doubt you can run anything higher than 147fsb from cold boot.