You can convert the map.
You have to edit the entities which you can do without decompiling the map.
Go here fo rmore information:
http://joe.to/cstrike/ents/
You will find information on converting a map from one mod to another and also information on converting from one map type to another, like making de_dust into cs_dust or what ever you want.
Two tools make this easier.
BSPEdit from the file base gives you a really easy way to edit the entities.
BSPEdit
BSPEdit_mm makes it child's play to add/remove/move the spawnpoints.
(but it currenlty only works running under cz, got to fix that..)
BSPEdit_mm