I want to create a split screen in premiere. I know that you have to right click and then click on the transparency thing and do all the stuff in there.

That part I get, but is it possible to do this:
I want one clip to play then suddenly it goes to the split screen and a line seperating the two clips comes up. What I do not know how to do is putting in the line. Is there a way to do this? Thanks in advance.

There are several ways to do this.

1 move your clips up 1 layer and split the screen leaving a gap between the clips and add a colour matte of your choice on the bottom layer, this will show through and create your line.

2 create a colour matte and crop it to the size your require and place over the join in your clips.

3 create a DV resolution, transparent image file in an image editor and add your line, save it to a format that supports transparency like .PSD or .TIFF and import this to premiere and add to the top layer.

I hope this helps.