Hi guys, total sponger here so apologies already .
I'm looking to build something that can go under my Sony Bravia 42" and run HD streaming video, music, and games at about a 360 level for as cheap as possible. I've also been told by the missus to move my classic console collection into the attic

/) so want to emulate pretty much every console out there so I don't have to give up my 16 bit gaming fix

.
Requirements are:
- Small (no optical drive needed, I have an external for installing things and a PS3 for playing Blu-Rays/DVDs and plan to use noCD cracks for my games that aren't Steam)
- Outputs in 1080p to my TV, plays games at a level that will hopefully match my PS3
What's the minimum budget I will be looking at? Can I do this for like £400? Also, can anyone recommend some good small cases that will not look out of place under the TV.
Finally,
what's the best software to pull all of this together into a neat little package? I want something I can control through a 360 pad and can handle email/emus/IM/browser/Skype/media management. XBMC looks like the ticket, but am I missing something?
Basically I want to make my own custom console :lol Any help would be greatly appreciated.