The File Replication Service, or FRS, is a critical component of an Active Directory deployment. When it has problems, it can be a lot tougher to troubleshoot than basic AD replication. There are some good Microsoft tools out there that can help. There are probably good 3rd party and freeware tools too, but these are the ones I am aware of. It is probably best to start with FRSDiag to get comprehensive information. Sonar is real useful for monitoring on a repeated cycle.
Keep in mind too that when you force AD replication using AD Sites and Services, that FRS is not included. With Windows Server 2003 (and a pre-SP1 patch) you can force FRS replication using the "ntfrsutl forcerepl" command. Patch here: http://support.microsoft.com/default.aspx?scid=kb;en-us;823230&Product=winsvr2003