Your laptop has got more than enough power to have your MP3 player and a sequencer package loaded simultaneously so you can instantly use whichever is appropriate.

You should be able to connect the laptop to the 740 using a "to host" cable (plugs into your serial port) and the Yamaha Serial port driver that can be downloaded from Yamaha. This acts like a midi cable and plugs into the mini-din on the back of the 740.

However, you may have to fiddle your power saving and/or mouse detection settings to ensure that the serial port can be used for the Yamaha cable. On an oldish Compaq Armada 7792 I've been given, plugging in my homebrew "to host" cable locks up the computer! I think this is a mouse problem but I haven't found the setup section yet! The cable works fine on my desktop machine.