To Upgrade or Not to Uprade

We have a small network of computer running Windows 2000 Pro. We have two servers running Server 2003 and Exchange Server 2003.

We’re also running a few legacy DOS-based programs.

I can see a future need to update to a newer operating system for the workstations, but the big question is when should we do it and which OS should we choose?

XP still seems to be the best option, but how much longer will it truly be supported?

Will the legacy programs work in the new OS?

Should I just sit back and wait for Windows 7?