There are numerous 865 and 875 chipset boards still available with integrated sound, LAN, RAID controller, SATA, USB, although you may have to check carefully for compatibility with the 400 MHz FSB series of processors, as some mainboards only support 533/800 MHz processors...
Although a 2.8Ghz unit, the 2.8/400 models will be handicapped by their 400 Mhz bus speeds, and easily outframed by 2.4/533 and 2.4/800 models
With that in mind, I'd recommend instead attempting to acquire both a much faster A64/3200+ and NF4 based PCI-e mainboard for about $250, rather than building a rig around/investing in an older AGP mainboard for what is a rather slowish $75 processor by today's gaming standards....