Marianne, I've benn using intensively the inage gals. (view, upload, delete, ...) during two Tiki courses I gave last week (finished them right now), and we have had exactly what you say.
However, the proplem happened even if we uploaded "small" image files (3 images at a time from different computers of ca. 30 Kb each). The Internet browser (MozillaFirefox 0.9.x) got stuck at the upload or at the image gallery viewing, and nothing else could be done with the Internet Browser. However, the server was ok, and the local computer also worked fine, except for the browser.
Later on, from another computer, I tried to clean things up from the image galleries, and My own computer Browser, from other building, IP, operating system (Win2k pro, Firefox 0.9) got stuck also at viewing the image gal.
See it at: http://uniwiki.ourproject.org/tiki-browse_gallery.php?galleryId=10
Increase file upload limit in php.ini? I don't have access to configure this in the shared server I'm using. How much should I suggest the admin of the server to increase this limit to?