Well according to the NVSS the Skyline R32/R33/R34 is already on the register thanks to Motorex! So safety wise the car is ok.
The only problem you may have is getting it to the emissions standards in your state, as that is down to state regulation. I am not an expert on state regs. Most Skylines are ok, but it will depend on the modification stage, for example if it running 600cc+ injectors and a modified air filter / Exhaust you may have some problems.
The import tax into the states is 2.5% (Hey UK guys look at this figure how cheap!), other state taxes may apply on registration though. If you want one from Japan, the going prices are:-
R32 GTR - Yen1,500,000+ (from auction up to 500,000 cheaper)
R33 GTR - Yen 2,500,000+ (from auction sometimes as cheap as R32)
R34 GTR - Yen 3,000,000+ (from auction cheapest is around 2,800,000 usually)
Remember R32 common as muck over here since 43400 were built, and now they are getting to the scrapping age!
R33 is a bit more exclusive since only 16,500 were built.
R34 figures very from magazine to magazine but there are RB26DETT (R34 versions) 22000 so far, some are after market though.