Mother Board upgrade advice

[cyberdad]

My present rig has a MSI KT3 Ultra2 main bvoard with a AMD Athlon XP2100 1.73 GHz and I am using a Radeon 9800 video cad. I mostly play with flight sim. My wife has an old Micron with a 600 megahertz CPU that she mostly uses for e-mail and web surfing.. What I am thinking of doing is: move my present MB, CPU and the 512 megabytes memory intact to her rig, and adding a larger capacity hard drive. Then I thought about upgrading my rig with something like the MSI 745 Ultra and a AMD XP2600 Athlon at 2.16 GHz. (selfish huh?) I have had good experience with the MSI board, but I have not kept up, and I am sure that there may be others out there as good or better. I can't afford the latest top-of-the-line. Any advice as to what I should use? Pitfalls?