Upgrading from source

[Arthur Barlow <arthurbarlow%earthlink.net@localhost>]

I'm new to NetBSD, though I've used FreeBSD for several years.  I  
originally installed the 4.0.1 version from CD.  I'd now like to  
upgrade the system to 5.0, but I'm clearly doing it wrong.  What I  
tried to do was create the "/usr/src" directory and then checkout the  
current version with CVS, by doing the "cvs checkout -A -P src"  
command.  This definitely updates the source, but when I try to  
install the userland section, it throws and error with a mention to a  
"-pthread" operation.  I used "./build.sh -u -U distribution."  What  
am I doing wrong?