I'm not sure if the above post helped you resolve your issue.
If not, go to DOS command prompt - change directory to winnt\system32 and run following
Regsvr32 /u Comcat.dll
Regsvr32 /u dtsffile.dll
Regsvr32 /u dtspkg.dll
Regsvr32 /u dtspump.dll
Regsvr32 /u dtsui.dll
The problem lies in that sometimes when you install new applications, they overwrite existing .dll files. However, when you reinstall SQL Server 2000 it won't overwrite existing .dll files.
Bear in mind that the above commands apply to SQL Server 7.0, and I'm pretty sure that there is at least one more .dll for SQL Server 2000.
There is a list of these .dll files in the Wrox book, Professional SQL Server 2000 Dts
by Brian Knight et al. Unfortunately I don't have the book with me here so I can't refer to it.
If you don't have the book someone might be able to let you know what the .dll files for 2000 are. If not, I'll post them here when I next get the chance.