Ok, neither of those systems are going to be any good for gaming as they both come with dirt cheap graphics cards. I would recommend ordering the parts seprately as this will save you some money.
www.overclockers.co.uk is great for this.
MSI K8N Neo4-F nForce4 (Socket 939) PCI-Express Motherboard (MB-053-MS)
Price: £59.95 (£70.44 Including VAT at 17.5%)
AMD Athlon 64 X2 Dual Core 3800+ (Socket 939) - Retail (ADA3800BVBOX) (CP-134-AM)
Price: £204.95 (£240.82 Including VAT at 17.5%)
Leadtek GeForce 7800GT Extreme Edition 256MB GDDR3 VIVO TV-Out/Dual DVI (PCI-Express) - Retail (GX-073-LT)
Price: £209.95 (£246.69 Including VAT at 17.5%)
GeIL 1GB (2x512MB) PC3200 Value Dual Channel Kit CAS2.5 (GE1GB3200BHDC) (MY-005-GL)
Price: £49.95 (£58.69 Including VAT at 17.5%)
Western Digital Caviar Special Edition 160GB 1600JS SATA-II 8MB Cache - OEM (HD-047-WD)
Price: £53.95 (£63.39 Including VAT at 17.5%)
Sony DWQ30AB 16x16 DVD±RW Dual Layer ReWriter (Beige) - OEM (CD-045-SO)
Price: £24.50 (£28.79 Including VAT at 17.5%)
OcUK Value Floppy Drive - White (HD-000-OK)
Price: £5.50 (£6.46 Including VAT at 17.5%)
Total: £714
Still need power supply and case though