Gang Prevention and Effective Deterrence Act of 2005 - Amends the Federal criminal code to prohibit various criminal street gang-related offenses, including participating in a criminal street gang by committing a predicate crime in furtherance of the activities of such gang, to gain entrance to or to maintain or increase position in the gang, or for the gang's benefit.

Amends: (1) the Controlled Substances Act to prohibit murder and other violent crimes committed during and in relation to a drug trafficking crime; and (2) the Violent Crime Control and Law Enforcement Act of 1994 to authorize the use of grants by the Attorney General to fund technology and training for prosecutors and to create and expand witness and victim protection programs.

Authorizes the Attorney General to: (1) designate high intensity interstate gang activity areas; and (2) expand the Project Safe Neighborhoods program.

Prohibits traveling in, or causing another to travel in, interstate or foreign commerce with intent that one or more murders be committed in violation of State or Federal law.

Expands the scope of predicate crimes for authorization of interception of wire, oral, and electronic communications to cover violations relating to criminal street gangs.

Modifies code provisions regarding the treatment of Federal juvenile offenders. Amends the Federal judicial code to direct the U.S. Sentencing Commission to promulgate and distribute guidelines for use by a court in determining the sentence to be imposed in a criminal case if the defendant committed the offense as a juvenile, and is tried as an adult.