Haesslich

For WM2003SE, both SPB and Sprite do excellent jobs - however, Sprite's got a few more backup options (selective restore, scheduling options) than SPB does... but the latest SPB Backup version is WM5 compatible and creates stand-alone .EXE restore images half the size of Sprite's. There's also SunnySoft Backup Manager, which does a decent job... although it's not the best option, it's less expensive than the Sprite Backup solution.

If you're going up to WM5, I'd probably get the SPB or Sprite software. The SunnySoft's not bad.. but it's definitely not WM5-ready, which will be important if you're going the upgrade route.