1.E8500 if you don't intend to overclock
2. You still need a case I would suggest a lian li or silverstone as they're excellently made with subtle styling compared to the more "bling" cases other manufacturers release. The page I linked to has some excellent mid-full size cases otherwise just have a browse through the entire case section. Save your spare pennies after that.
3. I could build it for you I am in Essex and only 40 mins away but email Graeme on firstname.lastname@example.org
to find out if they can build onsite they use to offer to
4. I have included a psu on the original list KustomPCs.co.uk - PC Power & Cooling Silencer 610 PSU
Btw that list of parts will run Vista like a pro but if your going to use xp you can scale back the ram to this KustomPCs.co.uk - Team Elite 2Gb DDR2-PC6400
as xp won't use the xtra gb's.
N.B. send me a pm if you want me to build for you