Hi,
can't answer all your questions but this may help. I run NT Server 4 (SP5) and use a Diamond Viper TNT2 32mb card and a SB Live sound card and all works fine. I am a MCP and built the machine myself using an Aopen HX08 full tower case with an overclocked celeron 300 running at 450 (runs solid as a rock) I used the Aopen AX6bc motherboard as it is a jumperless design and has recieved many favourable reviews. I cannot advise you on a dual processor board as I have not reviewed them. The Microsoft webiste has a HCL - hardware compatability list that may be worth checking out, don't use the one that comes on the NT CD as it is well out of date.
Hope this helps, all the best - Paul