This is hardly earth-shattering stuff, but just for reference.
There are multiple ways to grab PDB files from the RCSB PDB servers. If you know the accession code of a structure, the simplest way is wget (or similar) straight off the FTP or HTTP server:
FTP wget ftp://ftp.wwpdb.org/pub/pdb/data/structures/all/pdb/pdbXXXX.ent.gz HTTP wget http://www.rcsb.org/pdb/files/XXXX.pdb.gz
where XXXX is the 4-character PDB accession code.
Note the recent change of URL for the PDB archive: ftp://ftp.wwpdb.org. Note also the confusing 2, not 3 “w” in the URL.