Is there a way that I can tell Chrome (Windows, 5.0.342.9 beta) to remember my pinned tabs or preload tabs and pin them (when I launch Chrome)?
No you can not remember pinned tabs in chrome.
Since chrome is considered stable and released, they are still working very hard to improve and fix things. It's possible to remember tabs, and open them etc. There even are really usefull session managing extensions.
But it's not (yet!) possible for extension developers to create new pinned tabs. No problem to automatically open your favourite websites and open them in tabs, just not possible to pin them.
Chrome developers have found this functionality requested an awful lot of times and it's been mentioned in future milestones etc. So work is on the way! I might even release an extension myself when the time comes (thanks for the good idea)