Yeah, I would tell them what you want just to make sure. Or, if you're feeling adventurous, you could just do it yourself. Hooking up A/V components isn't too hard as long as you have the proper cables with the proper lengths. If you want to make them hook up your stuff (while they're already there), then I'd give them the cables you purchased (some high-quality stuff that I recommended before). Most of them installers carry bargain-basement cables. While that's generally fine for short runs of audio where there won't be interference issues, video is another story. A set of high-quality cables can make a difference in transmitting the signal without interference or noticable loss. High-quality doesn't mean expensive, but something made to proper specifications and with good-quality parts. Basically, don't waste your money on Monster. It isn't superior, it just costs more.
As a matter of convenience, I'd recommend that you have all the cables you need ready to go so the installation goes smoothly. The less time you spend behind your new TV fiddling with the connections the more time you can spend in front of it enjoying that big 50" picture.
Words of advice: take some time to organize your cables with some velco ties or something similar. It looks better, it's easier to deal with system changes, and it's also good to help keep interference out of your signal lines. Keep the power cords in one "trunk" away from all the other cables (speaker cables included) and if you must cross interconnects and power cables, then do so at a 90 degree angle.
Disclaimer regarding Monster Cable: Monster doesn't make bad products, but they charge too much for their stuff. Regarding my superiority comment, according to BMXTrix, a member here, Monster makes the best custom install speaker wire, hands down. He however, buys it for cheap on eBay, so it isn't much more expensive than competing brands. So basically, if you own Monster cables, don't throw them away, but if you need new ones, there's no need to go out and spend extra because they have "MONSTER" on them (unless you want awesome custom install speaker wire, then hit up eBay).
