said by Serbtastic:
Risky how? And what else would I need from L&M in order to connect the laptop's headphone 3.5 mm jack to the board?
Usually you don't want to run an unbalanced audio signal more than 25-30 feet. Running it longer than that exposes you to the risk of noise interference (eg. hum, buzzes, etc), particularly if the cable is run closely to AC power cables. Furthermore many audio output sections from laptops can be very noisy, especially when you plug the laptop's AC adapter into the wall! Blame it on the cheapening of audio components in many modern laptops today. They may sound fine with just a pair of headphones plugged into the output jack, but as soon as you plug it into a sound system, things worsen.
To play it safe, I either use a stereo direct box to convert the unbalanced source to a balanced one (keep the unbalanced portion as short as possible), or get a USB/Firewire based Audio I/O box that has a balanced output.
If going the stereo direct box approach, make sure they supply a 1/8" mini stereo cable to plug into the direct box (shouldn't be more than 10 ft long), and then two 50 ft XLR mic cables to run from the direct box outputs to the mic inputs on the mixing console. If you're going the audio interface route, then you just need the XLR cables, but before leaving the store, have them help you set up the software on your laptop to ensure the audio interface is working correctly with the laptop.
Here's a couple examples of decent stereo direct boxes:
(converts it to mono)
And of course a plethora of USB/Firewire audio interfaces from Roland, Presonus, etc that are available from their recording department.