On this page you find the compiled binaries for GRASS on Solaris 2.6 platforms. You just have to unpack the package, change some entries and use GRASS.
The binary package:
Usage: sh grass421install.sh grass_binpackage.tar.gz [dest_dir] with: grass_binpackage : name of GRASS 4.2.1 binary package optional: dist_dir - FULL path name to the installation directory default path is /usr/local/grass42/ Example: sh grass421install.sh grass421_solaris26bin22.tar.gz You may need to login as root for installation.