In a word: No.
Erich is right. Once a cop has a warrant, they can come in. If you try to get in their way, they can basically beat you into submission, then arrest you, THEN come in. (That whole, "duty not to interfere with police investigation" thing...)
If, after the search is done and the evidence is about to be introduced, your lawyer determines that the warrant was not valid, then all evidence obtained through the warrant (including all evidence produced through leads learned while executing the warrant) are inadmissible as evidence against the owner of the property.
Key phrase here is, "against the owner of the property." If person A is selling crack out of person B's house, and the police raid the house without a valid warrant, they can introduce the evidence to convict person A, but NOT person B. It makes for some interesting tactical decisions by the cops...
Get it?