Is this "stalker-esque"?

There is a woman that I am interesting in asking out; however, she is not really in my immediate circle of friends. I do really know anyone who knows her well enough to find out if she is seeing anyone currently. We met through various work events and I end up seeing her or working with her once every couple of months.

Tomorrow she is going to do some work for a guy that I work for in a town about forty miles away. I have debated making the drive down there to arrange a way to "drop in" on my friend while she is there just to create an excuse to test the waters on asking her out. This would not be my whole reason for going down there, though. I have friends who live in the town and I have been invited to an event later in the evening.

This is a long explanation, but I do not want to approach this in a way that might be creepy. I really like this woman and would like to get to know her better. Given our circumstances, however, it is really hard to casually create opportunities to chit chat and engage in normal flirtation. I feel that in this respect I might have to make my own luck. Ladies (or guys), where is the line between flattering interest and creepy interest?