Having installed the VMware Tools into my newly created Solaris Express VM, I discovered that the X screen resolution was absolutely massive (something like 2000x1000 pixels). The solution was to edit /etc/X11/xorg.conf from a command line login and remove the unwanted Modeline entries. As I wanted to run my VM in 1024x768, I removed all other lines, and then exited the shell. When the desktop manager reloaded, the screen was at the desired resolution.
The second problem was that installing the VMware Tools changed the network device from pcn0 to vmxnet0, but the /etc/hostname.pcn0 file remained and a new file was not created. I renamed this to /etc/hostname.vmxnet0 and restarted networking (rebooting will also work!).
Sendmail complains if it does not have a fully qualified domain name. The easiest fix it to edit /etc/hosts and add on a domain name alongside your host entry.
These are fairly minor changes than need to be made and the installation is looking pretty decent so far.