They seem to be extracting fine on my machine.
Did you try redownloading the files?
And are they named right?
If you want, here's the list of names and sha1sums I got for the files available for download (and don't worry, sha1sum is just a way to compare files, and no copyrighted data is included):
15d8e2dc2953eb2ced24daa08275c851788f6337 FirstTasteV1.part01.rar
1edc250c978268d1d2c74415f2fee248c7eccfb5 FirstTasteV1.part02.rar
3cea4dc95a9a1a2462f62f158daba4ae1de7c5d3 FirstTasteV1.part03.rar
abb415c35aab15b9f8dd9ab3cd676706f2e0e2dd FirstTasteV1.part04.rar
1d963448369089c709776e76c564bf39774bbafe FirstTasteV1.part05.rar
880a83ebc3644f919e331f9f777f3e22129e4fa0 FirstTasteV1.part06.rar
45367056a5600e944f6fee022888f26dd12a9087 FirstTasteV1.part07.rar
76c34c23d453c9c67e987352333d8d58f8f0c99d FirstTasteV1.part08.rar
f8e5257fb4e13f4dfe05fcf4817b61585219a59d Quest2 Build_1.5.part1.rar
2924a5fbeb5767bd51e50fa5b4dcbe97c3c30b29 Quest2 Build_1.5.part2.rar
c71d1edae0f7f01a3a3df0dac5f56aa9721ee59e Quest2 Build_1.5.part3.rar
fbe12611c68bd13658e9f0d81b4b560878f399fb Quest2 Build_1.5.part4.rar