What will he be doing with it?
EDIT: Try this (all prices include VAT, from Overclockers UK):
AMD Sempron 64 2800+ 1.6GHz (Socket 754) CPU - Retail (CP-138-AM)
£46.94
MSI K8N NEO-FSR V2 (Socket 754) Motherboard (MB-062-MS)
£49.29
Corsair 1GB DDR Value Select PC3200 CAS3.0 Kit (2x512MB) (VS1GBKIT400C3) (MY-061-CS)
£56.34
Western Digital Caviar Special Edition 120GB 1200JB ATA-100 8MB Cache - OEM (HD-001-WD)
£45.77
Leadtek WinFast A340TD GeForce FX 5200 256MB DDR TV-Out/DVI (AGP) - Retail (GX-027-LT)
£39.89
Antec Super LANBOY Aluminum Super Mini Tower Case - No PSU (CA-012-AN)
£34.02
Antec TruePower 2.0 430W PSU (CA-030-AN)
£51.64
Asus DRW-1608P2 16x16 DVD±RW Dual Layer ReWriter (Beige) - Retail (CD-017-AS)
£29.32
Total comes to 353.21 (wow, I'm underbudget!). So you could get a better vid card or something...