You're better off using an image for your dynamic lines. Create a 1 pixel x 1 pixel GIF in the color of your choice. In your img tag, you can specify the desired height & width.
FYI - less than 1% of all users worldwide use NN4+, and this number is getting smaller each month. If you don't have to satisfy a specific client, I wouldn't bother trying to support it in your code.
There's always a better way. The fun is trying to find it!