Just to add to Tom's response a little bit. I believe that the way to go is:
- Install SQL 2000 (which will we a challenge, because you will need to find an OS old enough to support it.)
- Restore the database.
- Upgrade the instance to SP4.
- Backup the database.
- Install SQL 2008 and apply SP4.
- Restore the database.
- Back it up a new.
- Now you can restore on any version from SQL 2008 and up.
To give you a little more hope, I should add that I am not 100 % sure that steps 1-4 are needed. I believe at least SQL 2000 SP3 is needed for an upgrade, but maybe that is only if you are upgrading the instance. So maybe SQL 2008 will accept your backup. Maybe.
(Bear in mind that it was a long time since SQL 2000 was ruling the world, so our memories are somewhat foggy.)