i too brought a setup without ever trying snowboarding (previously a skier), and spend a total of $400 on equipment (new boots, used board and bindings) ... about $150 on safety stuff (helmet, impact shorts, knee pads etc.) ... and already had outerwear from previous years (always preferred baggy clothes on the mountain).
after my 1st day on the hills, i learn to appreciate my own equipment. no rental line ups (for all of you), smelly boots, and other issues with rentals in general. it is sooo much better to be able to learn with your equipment (some kind of continuity) and of course being able learn with a whole bunch of friends is just a bonus. i agree with some of the other posts, as long as your friend has the funds for it and you have already given him your two cents on the issue. then let it go!
just jump on to the lifts together, take a drink from the flask (if you like), and enjoy! there is no better time to be with friends then on the slopes!