I've got a VM of Solaris 10 working pretty well for me. The installation itself was a snap -- installed right from the Solaris ISO I downloaded.
Once I manually installed the network driver (RTL8029) off the Parallels Tools (Other) image , the VM became accessible on the network. I'm masquerading using "Shared Networking" with DHCP so the VM has a 10.211.55 address.
Video modes were an issue -- took me several hours to get that usable. It comes up by default in some huge resolution which causes Parallels to enable the scroll bars. The trick is to generate a xorg.conf file using /usr/X11/bin/xorgconfig (puts the config file in /etc/X11).
There are significant issues with Solaris and a newly-configured xorg.conf file. As far as I can tell, you don't really know how it's going to behave until you actually reboot Solaris (DON'T just kill the X-server and let it restart). I went round-and-round (and round) with apparently bad resolutions (the X-server died when I tried to log in) -- rebooting seemed to be the solution. Right now, I have the VM running on an attached monitor, Full Screen @ 1600x1200. No guarantees, but here are what I think are the important parameters (NOTE: DON'T use these on a ~real~ monitor, only for the Parallels Virtual Machine' monitor):
(incomplete xorg.conf)
Section "Monitor"
HorizSync 0-250
VertRefresh 50-70
...
Section "Device"
Identifier "Generic VESA"
Driver "vesa"
...
Section "Screen"
Identifier "Screen 1"
Device "Generic VESA"
DefaultDepth 24
Subsection "Display"
Depth 24
Modes "1600x1200" "1280x800" "800x600" "1440x900"
ViewPort 0 0
Virtual 1600 1200
EndSubsection
...
Note: Switching resolutions on the fly (w/ gnome-display-properties) appears to be quite broken.
I haven't tried to get sound working. I don't think they have Shared Folder support yet, but you could NFS if you wanted to. I've been successfully SFTPing between my Mac and my VM to transfer files. Don't think they have mouse integration working either.
I've configured the VM to use both of my CPUs (and it seems to be taking advantage of them). The VM is also configured to use 768MB of memory (and I think it is). I have the Adaptive Hypervisor enabled and Parallels is optimized for the virtual machine performance. I optimized power consumption for "better performance."
I'm using Parallels Desktop, Build 4.0.3844. My VM host is a MacBook Pro 2.0GHZ w/ 2GB RAM, running Tiger (10.4.11) with the latest software updates. My installation of Solaris is: SunOS 5.10 i86pc i386, installed from the sol-10-u7-ga-x86-dvd.iso.
Hope this helps somebody.