table Presentation
int id
varchar name
int fk_template (references template.id)
...

table Template
int id
varchar name
...

table Position
int id
int zorder (if it is the 1st, 2nd, 3rd position of the given template)
int fk_template (references Template.id)
...

table Asset
int id
varchar name
...

table AssetForPresentation
int fk_asset (references Asset.id)
int fk_presentation (refernces Presentation.id)
int fk_position (ferences Position.id)

CREATE TABLE templates
( id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT
, name VARCHAR(99) NOT NULL
, otherstuff ...
);

CREATE TABLE presentations
( id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT
, name VARCHAR(99) NOT NULL
, templ INTEGER NOT NULL
, CONSTRAINT pres_templ
    FOREIGN KEY ( templ ) REFERENCES templates ( id ) 
); 

CREATE TABLE assets
( id INTEGER NOT NULL PRIMARY KEY AUTO_INCREMENT
, name VARCHAR(99) NOT NULL
, type TINYINT NOT NULL -- 1=img, 2=flv, 3=doc, etc.
);

CREATE TABLE presentation_assets
( pres INTEGER NOT NULL 
, asset INTEGER NOT NULL
, zorder TINYINT NOT NULL -- 1=1st, 2=2nd, 3=3rd, etc.
, PRIMARY KEY ( pres , asset , zorder )
, CONSTRAINT presasset_pres
    FOREIGN KEY ( pres ) REFERENCES presentations ( id ) 
, CONSTRAINT presasset_asset
    FOREIGN KEY ( asset ) REFERENCES assets ( id ) 
);