Looks like it's been compressed in WinRar format, and you'll need to decompress it. There's a freeware .rar unpacker here: http://www.tugzip.com/
TUGZip is entirely free, and what's more, deals with ZIP, 7-ZIP, A, ACE, ARC, ARJ, BH, BZ2, CAB, CPIO, DEB, GCA, GZ, IMP, JAR, LHA (LZH), LIB, RAR, RPM, SQX, TAR, TGZ, TBZ, TAZ, YZ1 and ZOO archive formats. That's quite handy to have if you plan on downloading often.