I had the same problem migrating data from SQL 2005 to 2000. I couldn't attach, restore or bcp. I resolved it in two steps
1) Copied Table Data from Sql 2005 to SQL 2000 using the 2005 Management Studio. It copies the table but not the PK, indexes, constrains..
2) I downloaded http://www.red-gate.com/ and used the SQL compare to identify and moves the PK, indexes, constrains, sp, views, triggers, ... with just few clicks.
FYI: you get the red-gate for 15 days trial and it is cheap.:D Also it is very easy to use the red-gate apps