I have little experience in migrating dts to sql2005, but I don't envy you for having 400 dts packages to migrate!
My info says you can do the import only one package at a time.
However: why do you want to import the packages in the first place?
AFAIK you should be able to export all packages to the filesystem from SQL 2000 (I think there are scripts around to do that), and then run the dts-packages in the filesystem from SQL2005.
You would still have to redo your scheduling and so on, but I think you'll have to redor that when importing them as well.
Another option might be to do an inplace upgrade of your SQL Server, which (according to some sources) would keep your packages in running state etc.
Hope these alternatives can be an option to help you.
BI Consultant, The Netherlands