£400 to upgrade my HTPC

[Spider]

I currently have a Coolermaster Cavalier case housing a P4 3.0Ghz HTPC running MCE2005. I have 2x500GB HDD, a budget ATI 128MB video card (VGA into a SD Plasma), onboard sound (SP-DIF into my receiver), Nova-T DVB-T dual-tuner TV card and 1GB RAM.
This has worked fine and coped admirably with the HTPC use (its never used for gaming or anything else) and is our ONLY source of TV in the house. No Sky or freeview box but im starting to get a bit narked with MCE2005 and would like to upgrade it to Vista MCE with a view to distributing the media around the house.
I'm therefore going to upgrade the machine to a better spec that will future proof things a bit, as my next purchase if a 50" HD Plasma, so I want something for now and then.
I don’t mind if It’s a completely new build from scratch (would like to keep the HDD's and the TV-Tuner though!) or just replace the CPU/Mobo/RAM/GFX and keep the case and all other components.
I would like the system to be as quiet as possible.
Can anyone suggest the best path to take for this upgrade?

Gracias!

 

[Spider]

Thanks for that, lots of really useful stuff there.
The reason I’m moving to vista is im sick and tired of MCE2005 losing my channel line up. It seems to be happening several times a week now and meaning the machine has to be rebooted regularly or programs wont record! I believe this is resolved in vista so that alone is enough reason for me to move. I already have a copy of vista I bought for my home machine that I don’t use, so the cost wont be a factor.

I tried mediaportal a few months back - couldn’t get on at all with it. It wouldn’t play a thing and couldn’t get it resolved, even by posting the logs on the official mediaportal forum no one could resolve it so I thought enough of that!

I like the sound of that motherboard with all that on…Could use the VGA for now and HDMI when I upgrade the screen later in the year.

Im concerned about the noise issue with AMD’s though. I want something that’s going to run as close to silent as possible as that is where my current build kinda lets me down I feel (and partly why I was thinking of getting a new case…)