I'm using PhotoShop 7.0 to paint. I'd like to hear some input on what tool to use to make curved lines.

Use the line tool. You can use the point to wich will allow you to do simply that, go point to point around a curve. If you want a real fluid curve, use the beizer line. It is a little tricky but once u get the hang of it it works well.Ill give u a little tip on how it works.Left click once to make a starting point. That point should be filled solid white (if not, just click on it again). The next dot is where u have to make a decision. If you want a curved line between your "start dot" and you "next dot", left click once but hold the button down until the curve tool appears. Then u manipulate the line with the tool. If you want a straight line from "start" to "next", u simply left click and release the button. To continue the line, you just go from point to, and repeat the step and make a point 3 etc.... You can make a straight line or inject a curve anywhere in the series. You do however have to make it a straight point or a curved point before you move on to next one. When you have made the line the lenght you desire, CTRL-Q on the last dot will finnish it.Hope this helps.