G'day mate!
Okay, if you wanna start marines then I reckon your best option is to get the Assault on Blackreach box. The marine models are pretty good, you get a bunch of units you will use, plus all the templetes dice and rulebooks you need. You even get some orks that you can either sell or crush with a brick like I did because they are Xenos scum.
As for Imperial Guard, my army of choice, get a battle force box to start with because its good value and you will need everything in it to begin with.
I'd suggest more, but either army has a huge mix of units, most awesome, but some not so great when used in the wrong way.
As for the codex books, seriously, don't buy jack until you've at least read through them. If your serious about starting, go to a
GW store and ask them the same question. In your country I hear they totally barrage you with sales crap, but they will have copies of the books you can leaf through and get an idea of what can do what. Then buy one or the other...or both is better. Read them backwards and then decide.
IG is one of those armies that can get very large, very quickly, and if you make the wrong choices it will cost you twice as much money.
Marines are a bit more simple, in that because they are a more expensive army point wise, this means you have to buy less.
Good luck mate, get buying!