get a faster HDD or turn off all the active window anitvirus crap. the bottleneck when extracting something is how fast winrar can write to the HDD. either yours is slow to begin with, or you have some bullshit active antivirus that is scanning your HDD at the same time you are writing all this huge file to it, or a combination of both
Ummm, weirdness to be sure. I would try and use 7-Zip and see if the same problem persists. May just be a problem with WinRAR. BTW 7-Zip is safe, free, and open source in case you haven't heard of it.
EDIT: A thought crossed my mind. Is this a scene release off of usenet/newsgroups? It may be a corrupt download and you might have to repair it provided if you have the parity files to go with the archive set.