Epox 8RGA+ 88.87
XP1800+ 39.43
Corsair Value PC2700 256Mb 30.92
Cooler Master Fan CP5-7JD1B-0L (XP2800) 10.08
Q-tec ATX Midi Tower Silver Case (300W) 29.30
[+ 450W Q-tec PSU maybe....] 26.20
Maxtor DiamondMax plus 8 7200RPM 30Gb 40.31
CDROM/DVD/CDR - steal from old machine.
Total 265.11
Prices from Komplett.co.uk
If the 300W PSU in that case is sufficient, then that'll be 238.91 instead, but I would strongly suggest getting more power... I have built a system around a Q-Tec PSU, and found it was fine, but that was a 450W one, NOT the 300W one that comes in that case.
This system will have some room for overclocking - he should be able to just raise the FSB to 166, to give a speed of 1.9 Ghz (XP2400+ [ish]). The chip would easily cope with more Mhz, but the cheap RAM and HSF would be holding you back.
The Mobo has Built-in sound (NForce APU - better than most add-in cards) and built in Vid Card (Geforce 4 MX).
When more money is available, he can shove a Decent GFX card into it too, as it has an AGP slot.
Seriously though, tell your mate to wait and save another £150, and He'll be able to get a much better system - a decent cooler (£25) and at least 512Mb of high quality RAM (corsair PC3200LL 512Mb - £130) and he'd be able to squeeze more performance from it.
But the above system, at stock speeds, will be able to play all the recent games etc. at acceptable detail levels, and will have some headroom for upgrades. You don't list all the parts he has available from the old system, so I'm assuming he at least can get a CD-ROM and an IDE cable from it.
HTH
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$hit Happens. I just wish it would happen to someone else for a change.