Backup Exec 10d does support backups of SQL 2005 server. However, Backup Exec's database cannot be installed on SQL 2005 server. This is the reason why, environment check is not finding MSDE or SQL 2000 installed. I suggest you to install Backup Exec using it's own MSDE instance.
I'm having the same problem. except when I try installing BE using its own MSDE it keeps rolling back. I had it working fine but then someone installed SQL 2005 on the server which messed up the MSDE 2000 install. Any tips