hi ive completed fallout 3 on my xbox 360 and i just want to go through the game again with cheats for a different experience, you know like all weapons and infinite ammo is all. do i use G.E.C.K. or just use in game console commands

Just use in-game console commands. Here is some useful ones:
tgm - Makes you a god: You can't take any damage, you have unlimited ammo (it reloads instantly) and you can carry unlimited weight.

tcl - Makes you able to fly through everything. Write tcl again to disable.

player.additem <base_id> <amount> - add item to your inventory

player.moveto <ref_id> - move player to NPC

moveto player - move NPC to player character

resethealth - restore NPC's health

kill - make NPC die.

resurrect - resurrect NPC

tcai - toggles all combat AI off/on

tai - toggles all AI off/on

setally <factionID1> <factionID2> (0/1 optional) (0/1 optional) - sets a faction as an ally with another specified faction. 0=Ally 1=Friend

setenemy <factionID1> <factionID2> (0/1 optional) (0/1 optional) - sets a faction as an enemy with another specified faction. 0=Enemy 1=Neutral.

setessential <base_id> 0 - make NPC mortal

setessential <base_id> 1 - make NPC immortal.

player.placeleveledactoratme <base_id> - create/clone an NPC and place it at the player

player.addperk <variable> - add a perk or trait

player.removeperk <variable> - remove a perk/trait

player.advlevel - advance one level

player.setlevel <level> - set level

player.rewardKarma <amount>, player.rewardxp <amount> - give player Karma or XP

setownership - make the item yours.

player.placeatme <base_id> <stack amount> <quality> - place an item next to the player

ok thanks for the help just bought all the weapons from the guy outside megaton then killed him mwahahhaa :P

You're welcome. I actually found another cheat you might find useful:
coc testqaitems - Warp to room with all items

coc megatoncommonhouse - Exit testqaitems.

problem with the all items thing is i cant unequip the weapon and its a lame knife

ok thanks i just got the items and stuff and blew up megaton :P mwhahahaa

Much needed thread.

is there anyway to start the game with all weapons,

I don't think it's possible. There are tons of different weapons in this game. You can however use the command line to add the desired item to your inventory. Check this guide: https://fallout.fandom.com/wiki/Gamebryo_console_commands.

wats the id for the pistol, and i tried using the geck to start with weapons but itl ooks to complicated

What kind of pistol do you want? If you're talking about ordinary 10 mm then it's 000434f. You can check multiple ids on this site: [url=https://fallout.fandom.com/wiki/10mm_pistol_(Fallout_3]https://fallout.fandom.com/wiki/10mm_pistol_(Fallout_3[/url]). Just search for the weapon you're interested in and check the code in the table on the right side of the screen.

whats the item id for the shit knife u cannot unequip and also can i teleport out back to vault 101 with all items

I recommend FO3 over New Vegas because the New Vegas changes are so noticeable that you'll be bothered by their absence in FO3. You won't notice them as much if you first play FO3.

They're both fantastic, though, and the DLC is well worth the extra cash for GOTY/Ultimate Edition. Check here https://cheatcommands.cc/fallout-3-console-commands/