hi mate and welcome to this damned lovely place, seriously.
you'll prob come under-fire from both the mac and pc 'side' of things when it comes to buying a laptop - try both if you can and see what feels most comfortable (operating system wise). i've recently gone mac after using pc's for years, but most of my reasons were down to stability and all my friends having macs/running logic so it became more and more difficult to share files easily, etc.
i'm not saying pc's aren't stable, it was prob my own lack of 'housekeeping' tbh - and some bits of my pc i really miss, but the mac is cool, and has enough grunt to keep me going for a few more years. i was at the point of having to upgrade the pc anyway.
software - this bit can be the part that decides which laptop/os you opt for anyway - as i mentioned, i missed using logic and going mac meant i can now use the latest version instead of using an old and buggy pc one. that said, i got into using cubase sx3 for a year or 2 and it's pretty awesome. macc and a good few others on here use it which speaks for itself and i really miss its very powerful handling of audio, for example - much more powerful than logic for editing audio etc, but then i always felt more natural when actually 'writing' in logic, if you get me?
you can always get demos of these sequencers, like try cubase out on your net pc for now, just to see how it feels in use. other options are aplenty, like ableton live, sonar, reason, tracker programs, modular progs like buzz and audiomulch etc etc. this all gives you plenty of choice (prob too much
) between quite expensive top end progs and completely free packages, too.
basically - logic and cubase are deep and quite intensive to begin with, but well worth persevering with - ableton is more simplified and will let you stretch audio very easily (so you can make a sampled drum beat line up in time, regardless of tempo) and also makes other obvious things very simple, so you can get stuff moving quickly. that said, i always feel frustrated by the lack of midi editing options that ableton offers, but that prob comes from being spoilt by logic/cubase for too long. people like cycom and martsman use tracker programs to make their amazing stuff, but i've not used one of those since the amiga days, so i can't speak for that side of things, sorry!
soundcards seem to be falling out of peoples pockets these days, there's so many of the bloody things! like with your whole question, what you opt for/spend is dependant on what you want to get back out of it, and equally as important, what you want to spend getting there.....the quality you get for not too much cash these days is absurd compared to only a few years ago, so i'd prob start off buying something from a reputable make, but i wouldn't get drawn into the 'i must spend £350 or it's gonna be shite', cos that's utter bollocks. hell, you could even use the internal soundcard on a macbook if you wanted to, until you got some more cash to buy a usb/firewire jobby. not ideal, but more than useable, my mate's done live gigs on his after his posh rackmount tascam fucked up on him, and it went fine
for making dnb/jungle without recording a live band at the same time, i'd prob just get something with a couple of inputs, prob a few more outputs, portable and bus powered, and with a headphone out so you can write in bed if the mood takes you, without getting grief off the missus
so yeah, decide what your budget is - that might get you a lot more recommendations for specific gear on here mate - demo a good few sequencers but give each a bit of time, as opposed to an hour before giving up. follow the tutorials! search the net if you're stuck on something, or the bundled manuals! get some samples ready beforehand so you can try out that side of things straight away, as it's an important area. most sequencers come stuffed with effects and virtual instruments anyway, so you shouldn't have to worry about that. remember that you can demo the software on any (pc) computer without a posh soundcard by getting a free program called 'asio 4 all', which will let you run high end audio shit on a built in (shit) pc soundchip. the mac soundcard will run the better audio sequencers by default anyway. then when you decide you are into it and are gonna kick breakage's arse with your tracks, you can start looking into soundcards etc
so;
pc v mac - both do the same things, differently. that's it. pcs are more budget friendly, but less component friendly, due to 3rd party/non matched stuff they can be configured with, or that you might add yourself (clashes, etc). there are a lot more free/mad programs/fx around on windows though, but ironically i'm getting more done now as i'm slightly more limited. plus you can always run windows on a mac, using parallels or bootcamp. worth looking into. but, both do the same job at the end of the day.
soundcards - don't spend a fortune (for now)
software - try, try, try. free demos are rife, get em all and try making a track on each one. if it feels like you've put an old pair of slippers on after an hour or two, you're prob getting warm. don't be disheartened if it all sounds shit, you'll get better and better at it with time anyway, and i'm sure even the best producers write piles of complete turd, inbetween the killers. just persist and you'll get a feeling for which one is the most natural for you.
phew. hope this helps mate, and good luck
much love, hovver
oh fuck, we forgot to mention monitors........