You could try using 3D-Analyze in Virtual PC/XP Mode. It's supposed to emulate 3D accelerated graphics.http://www.3dfxzone.it/dir/tools/3d_analyze/index.php
However the requirements for graphics memory for RealMyst are 16 MB and Virtual PC/XP Mode only supplies 8GB. So Myst IV and V won't work in XP Mode/Virtoal PC.
If you want to try XP Mode, you can get it herehttp://www.microsoft.com/windows/virtual-pc/download.aspx
And here's a site that tells how to install it.http://windowssecrets.com/top-story/using-windows-7s-xp-mode-step-by-step/
I'd recommend using Windows 98 inside of Virtual PC instead of XP Mode. That way you can keep your VM's (and QuickTime versions) separate.
Myst Masterpiece and Riven do not require any hardware acceleration and I think Myst III has an option for software acceleration, so those three should work in Virtual PC with Windows 98. The copy "protection" may be a problem though.
However I don't think you're going to get any of those games going on Windows 7 without a lot of fuss.