The general recommendations for hangs of this sort are:

1. Make sure your application is up to date (and make sure any applications used by the main one are also up to date...in this case, the Quicktime 6 suggestion is a good one)
2. Make sure all your drivers are up to date. A bad driver is much more likely to cause a sudden reboot instead of a hang, but you never know.
3. Find out what else is running in your system. Run a spyware and virus scan and then shutdown things like virus checkers, messenger apps, etc. (not permanently, just close them while you experiment). You never know when someone's random app is inappropriately locking a resource that Poser might need in the system.
4. Make sure Windows is up to date. Use Windows Update to ensure this
5. Try creating a new account and running from there. Sometimes things get screwed up in user-specific settings and a new account is as good as a reinstall of Windows when that happens. Also, consider setting up this account as "Limited User" instead of an "Administrator"...many badly-behaved apps (both malicious things like spyware and just poorly written apps) will fail to run and consume resources when you aren't running as an Admin, and if one of those is interferring, this can help identify the problem.
6. If all else fails, reinstall the OS.

If, after a complete reinstall, you still have the problem, you should probably start looking into the possibility that something is wrong with the machine itself (though such a thing would usually show up in other apps, graphics apps like Poser do tend to tax your computer in ways that simply checking e-mail or browsing won't).