Is there any possible way that I can bypass the main quest line up until the player arrives at The Citadel or whatever it is called? The reason why i ask this is because I played through the early parts couple times before but once I get to the Citadel I eaither stop playing or run into problems and I really don't want to play the early parts again. So is it possible to bypass the early parts with like a savegame or a cheat?

You can start by heading straight to Vault 112 and picking up the main quest from there - this doesn't require any cheats even.

You can skip straight from escaping the vault to the Tranquility Lane quest by going to Smith Casey's Garage but you'll still have to get Dad out of there and complete The Waters of Life.

Alternatively, http://fallout3nexus.com/downloads/file.php?id=12729 from Nexus that starts just before Take It Back.

Edit: Bah! Ninja'ed again.

Well actually tranquility lane was the whole reason why I wanted to skip to the Citadel but how long does it take to do the quests in between?

How long does it take to do Tranquility Lane and The Waters of Life and get to The Citadel? You can complete Tranquility Lane within a minute of getting into the pod, fast travel to Rivet City with Dad and then do The Waters of Life in another 20-30 minutes probably, assuming you know where the spawns are and don't stop to loot everything.

Tranquility Lane is probably one of the cleverest parts of FO3

In Tranquility Lane you can just go straight to the Abandoned House, hit the items in the correct order to open up the terminal, then activate the failsafe and leave. You never have to talk to anyone at all in there.

Yes - I love Tranquillity Lane!