Ok sorry for the crapy diagram here but let me see if I get this straight:
You have a network that looks like this:
Pineapple---[eth]---Laptop---[wifi]---HomeRouter---[adsl/other]---internet
And you want to limit the connectivity from your main "HomeRouter" this will in turn limit the connectivity to your laptop (as I am guessing you use a connection sharing setup at the laptop right?) and thus in turn this then filters down to limit the pineapple, this seems like overkill to stop leachers you could set up wshaper on the pineapple and shape ppl's connections.
Bert Huberts website (http://lartc.org/wondershaper/) talks about what it sounds like you want to do with the pineapple but if you want to do it to your whole network then yeah probably QoS rules.
Acording to this (http://tomatousb.org...to-s-qos-system) the main gist of QoS is more application based mannagement not individual client based mannagement. This does not sound like what you are after (read below)
If however you wanted to limit the total amount downloadable (say so as to not rack up a massive bill on your 3/4g carier) you may try this page (http://wiki.openwrt....acket.scheduler) and do it on the pineapple itself, your main concern seems to be that a client will suck all your data, you may wish to read more from our freind Bert Hubert, (http://lartc.org/how...artc.qdisc.html) Lots of theory on shaping there but I still think this would be best performed on the pineapple itself.
But then I have 0 experience here I just googled it.
Other than that see if you can monitor some one and just blacklist em after a limit is hit, if they change their mac addr to get back on then you probably have a bigger fish on the line than you want and you may wish to revisit wshaper.
There could also be software options for the laptop itself to limit the amount of bandwidth the pineapple, if windows there is a bunch of realy dodgy lookin free programs... as of 6 years ago there seems to be no way to limit bandwith in windows nativly (ref: http://www.techsupportforum.com/forums/f31/limiting-internet-bandwidth-over-lan-119444.html#post655275) and if windows is anything to go by I have no reason to believe they have fixed this yet.
Good luck.