Is it possible to "preload" all thumbs.db files in a directory?

You can "force" to create all the needed Thumbs.db if you do a search of all image files in your disk, and then set the view to "Thumbnails".

Thumbs.db is a caching mechanism. It stores the thumbnails so the system doesn't have to scan every file in the folder to get it's thumbnail. There's no way to cache it beyond that.

E: even though you're seeing the thumbs.db files, I would double check that the system is actually using them (and updating/generating new ones) by making sure Folder Options->View->"Do not cache thumbnails" is unchecked. Beyond that, I don't think you've got any options.

Concerning Windows XP: Doing a SEARCH for images (*.jpg, *.bmp, ...) and switching to thumbnail-view does only TEMPORARILY generate those thumbnails: NO thumbs.db file(s) get generated and stored!

But recently I found out a special trick that can be used for an automatization procedure (e.g. command batch-file): If you first copy a (wrong) dummy thumbs.db-file into a folder and open that directory with windows explorer in thumbnail-view, you now DON´T HAVE TO SCROLL through the directory any more to get all thumbs generated!

Certainly it will take some time, especially in huge image-folders, until your (slow) single-core PC finishes the generation of the thumbs.db file. When it´s generated, or doesn´t grow in size any more, you can recursively traverse to the next directory in your batch-file.