>The market here in Mexico is composed of many LAN installations with a mixture of WinXP, WinNT, WinME and Win 98 still now. Suppose that a client of you in this market ask you to develop a system that will be used at every computer in LAN. In this case, could we say that VB.NET is a good choice for this development?

Not really with older OS and hardware. I'm not sure if it will run in Win ME/98 but even if it does, the hardware would probably be too old, small and slow. They will need at the very least some memory upgrades. Any system with Win2000/WinXP/Win2003 should be OK (hardware-wise).