The gallery is weird like that. To multi-select for anything (share, move, copy, delete, etc), you select the function first, then it lets you select the pics/videos. So if you want to share several pics at once you first go to the album in the gallery holding said pics. Then tap the share button at the top right of the album and choose the app you want to share with. In the next screen you select the pics you want and tap NEXT. Then it will take you to the app you selected earlier to finish the process. Each app will obviously function differently, but should be straight forward enough at that point to figure out what to do. Like for Handcent, I type the contact name I want and then send.