You can view a load of Liberty City maps as part of the game. All you have to do is us a PC with an internet connection... Like in an internet cafe then use it to go to this website:

www.whattheydonotwantyoutoknow.com

Here you get access to maps with hidden items, weapons, friend locations, pigeons and jumps.

After you meet Faustin, complete ALL 100% of his missions, before attempting Dimitri's missions, as Dimitri has you kill off his best buddy Faustin. Therefore making him unable to give you his final lot of missions and you'll be unable to get 100% completion of the game overall.

Cheers to Superblobby on the SuperCheats forums for that one.

In GTA IV cheats are activated via using the mobile phone. Try entering any of the following codes after Roman has given you his old mobile phone. This happens pretty early in the game so you don't have to wait long before you can enter the cheat codes. Once you have the phone you can enter them as often as you like.

Okay, first get out your mobile phone and press x to raise the phone higher and reveal the complete keypad then use your controller to select the set of numbers according to which cheat you want to use, after you have entered the code the cursor moves to the dial button, just press x again and if successful you will see a message 'Cheat Activated' on the screen.

It's still early days for these cheat codes, so we advise you not to save your game after you have enabled a cheat code.

Full health
Call 3625550100

Full health and ammunition
Call 4825550100

Reset wanted level
Call 2675550100

Wanted level up one
Call 2675550150

Weapons 1
Call 4865550100

Weapons 2
Call 4865550150

Change weather and brightness
Call 4685550100

Spawn Annihilator cop helicopter
Call 3595550100

Spawn Cognoscenti
Call 2275550142

Spawn Comet
Call 2275550175

Spawn FBI Buffalo
Call 2275550100

Spawn Jetmax
Call 9385550100

Spawn NRG-900
Call 6255550100

Spawn Sanchez
Call 6255550150

Spawn SuperGT
Call 2275550168

Spawn Turismo
Call 2275550147

Super Cheats are putting together a complete guide to GTA IV. You can find our work in progress here:
http://www.supercheats.com/guides/grand-theft-auto-iv/

As we get further into the game we'll keep adding to the walkthrough so the first updates will be very soon. We'll keep going until we have a complete walkthrough with all the secrets revealed. So with that said, I suggest that you bookmark the guide and check back every so often if you want some GTA IV help.