Re: picking a new receiver
Pre-Amps are the "brains" of the system. They are totally necessary to listen to a speaker system and for any other video or audio signal processing. They also minimally boost the incoming signal (be it from cable, satellite, dvd, cd, Lp, tuner, etc.) so the amplifier can boost the signal for the loudspeakers. The Pre-amp (whether as a separate or as part of a receiver) also has all the decoding and the featuresets. Even your HDTV has a modest pre-amp in it so it can play without a full-blown audio system. But lets face it, it is pretty lame in comparison to a good surround sound loudspeaker system. Your enjoyment definitely increases many-fold when using a surround system with loudspeakers and a subwoofer.
If price isn't a huge obstacle, separates are often better. In these days of HDMI interconnects, connecting separates is hardly more difficult then on a receiver. On the pre-amp section of a receiver (or on the separate AV pre-amp) there are outputs for your speakers and a self-powered subwoofer.
As far as playing Blu Ray discs, you need a Blu Ray player (I recommend either the Panasonic DMP-BD35K, the Panasonic DMP-BD55K, or if you also want to play games--the Sony PS3 system).
You connect the Blu Ray player to either the pre-amp, the receiver, or directly to to HDTV with an HDMI interconnect. You can connect the Blu Ray player directly to the HDTV if you don't have your separates, your receiver, and your loudspeakers yet. This way you can at least watch movies before you get the rest of your system.
When you get the rest of your system it is then advisable to connect the Blu Ray player to the separate pre-amp or the pre-amp section of the receiver.
Your most difficult decision will be the type of loudspeakers and subwoofer and where you will place them in your room. For most people, a 5.1 speaker system is plenty adequate--even though most pre-amps and receivers have inputs and outputs for up to a 7.1 system.
In a 5.1 system, the .1 stands for the self-powered subwoofer, while the 5 part stands for the left and right front speakers, the center speaker (important, as it contains most of the dialog information), and the left and right rear surrounds. In a 7.1 syatem there are an additional left and right rear surrounds that are employed, but for most people are totally unneccessary. I have two 5.1 systems in my house and they are both great and provide much enjoyment for me and for the rest of my family and guests.
If you have other questions, don't hesitate to ask. I realize that it can seem imposing to a "newbie" that is just getting started.