So, I've done both; created the as-the-crow-flies lines that just go straight from the surface hole to the bottom hole and taken directional survey data and created the actual path the drill bit followed (sometimes referred to as the "worm track") to create the borehole. As-the-crow-flies is much easier, and as Kirk mentioned in a comment, the XY to Line Tool should do what you need I think. Basically, you want to connect the surface hole location (SHL) with the bottom hole location (BHL) - those two sets of coordinates for a directional/horizontal well are usually available. A few years back, I wrote some Python and created a tool to do what that does, as the XY to Line Tool wasn't around back then. So you ended up with something like this:
Now, as far as plotting the actual wellbore, if you can get your hands on the directional survey, you can use the azimuth and northing/easting of each MWD point to get a XY value for each point. So, like in the above as-the-crow-flies scenario, you are plotting the SHL and BHL, but also every other point in between. If you just need 2D, then the XY will get you that, if you want 3D, then you need to use the depth value (Z) from the MWD for each point as well. You can also M-enable the line which will allow you to plot the perforations along the wellbore. With this method, you can achieve something like the green lines below (apologies on the sloppy screenshot, had to cover up some info on it), where multiple wells are drilled from the same wellpad:
If you're lucky, the directional survey vendor might do some of the conversions of azimuth northing/easting for you already. Once you have your XY's (and ZM's possibly), then you plot the points in order from surface down and connect the dots to form the line. I did this in SQL Server 2008 Spatial before, and I'm not sure if ArcGIS has tools that can accomplish this out of the box; it could surely be coded in Python though.