Did you decompress the .sit file outside of the emulator? If so, there's going to be a lot missing, as Classic OSes (9.x and below) used files that often had 2 halves: the resource and data forks. PC's ignore the resource fork, and most Windows decompression programs just throw away the extra information. It's been awhile since I've done any Mac Plus emulation, but grab a copy of HFVExplorer and make yourself a disk image with it (preferably an 800k disk image). Use HFVExplorer to drag the .sit file into the disk image, and allow it to decompress the files straight onto the image. When you drag the file to the image, it'll ask you if you want to decompress it. Load that image as a second floppy disk in vMac, and hope for the best.
You may need to mess with the image settings in HFVExplorer a bit, though-- I don't remember if vMac recognizes the default .hfv images it creates or not.