intercept trouble

[Exitaph]

I'm having trouble finding the intercept point when trying to get to other planets. I'm using the interplanetary guide and calculator (http://ksp.olex.biz/), so I know that I'm leaving Kerbin at the correct launch window. Is there something I'm missing? Is there some trick to finding it?

I've been searching for hours about this but can't find anyone with the same problem.

[draeath]

You want your orbit to get as close as possible to the destination so that you are in the same area at the same time. So simply launching at the same time isn't enough, you need to put your apoapsis in the right place.

[Exitaph]

Well, right. I understand that. I'm having trouble figuring out where exactly to make my orbit cross the planets' orbit.