You can get a 500w psu that is decent for that price
Everything else seems ok to me I take it the mobo has on board sound without googling that mobo but I have to say I love m Asus board and the features etc but the sound software is a bit crap on them if it is sounstorm

 608274 Antec NSK4480B Black Mini Tower Case - EarthWatts 380W PSU £48.18
Nexus this is the case and psu, if he spends this much on a psu it will up the price by at least another £15-30 for a case

606949 AMD Athlon 64 X2 Dual Core 6000+ (Socket AM2) - Retail with Fan £96.35
Could try something with a little less power to bring the price down for other upgrades, i.e. case/psu

608233 Asus M2N-E SLI nForce 500 PCI-E SLi (Socket AM2) DDR2 ATX Motherboard £49.95
Why does he need an SLI board? Surely if he is spending £350 on a full system he wont be wanting to spend another £2-300 on a half decent set of of cards, i would go single slot and save £s for other upgrades.

605704 Corsair Twin2X 2GB DDR2 (2x1024MB) XMS2 6400 £46.99
change to this http://www.ebuyer.com/product/98710 and save a further £7, i reckon you chose the cl4 stuff. you can drop the price more by going generic.

607273 Seagate Barracuda 7200.10 SATAII NCQ 3Gb/s 160GB 8MB Cache OEM £32.89
Egg, dont know why he will need more than 160gb, i mean software and games wont take this space up

608079 Samsung SH-S202 20x Dual Layer DVD-Rewritable Black - OEM £15.98
Good call, could spend a little more for retail with lightscribe, you will also get nero etc then.

605557 Sony 3.5" Floppy Disk Drive Black - OEM £4.14
who uses these now ?

607546 Club 3D nVidia GeForce 8500GT Passive 512MB DDR2 DVI/TV Out (PCI-E) - Retail £54.05
Is ok but the savings on other items , you could upgrade this.
Total £348.52

Cheap PSU cos it works and does the job.
Cheaper CPU cos he wont know the diff.
Ditto cheap mobo.
Big hdd.
Decent GFX card cos this is eyecandy=moneywellspent.


edit: Case didnt go in the basket, so + £8 for cheap case that looks ok from the outside.

http://www.ebuyer.com/product/108273

edit2: I used that case for a build a while back and it was fine. Stuck a £3 cold cathode in it and my mate was well impressed.