FCP offers the most bang for the buck, hands down. It'll grow with you. From miniDV cuttin to uncompressed HD motion pitctures... it's one piece of software, you justa dd hardware as needed.
Vegas is awesome for the price. Certainly the most powerful tool in it's class and more audio strengths than most NLE applications above it.
Adobe Premiere is cheap, easy and capable. Hard to go wrong with premiere, after affects and photoshop.
I have an Avid Adrenaline HD.
It has over a terabyte of storage, genarts sapphire plugins, BCC effects, After Effects and photoshop. I will be selling this system next year and getting an uncompressed HD FCP system.
I edit for a living. With my work flow, there is very little need to spend more than 30k on a system today. If that sounds like a lot, it's not. The suites I bagan editing in were multi-million dollar rooms. Today, people get the same capabilities those suites had for a few hundred bucks at Best Buy.
I suggest out-growing windows movie maker first. It's great to begin on. If you dig editing, you will soon outgrow it and by then you will know what you want in a NLE.