I've taken apart old sewing machines to oil and lubricate, but never a serger. It's possible that it simply needs cleaning and oil or new lubricant; oiled parts can stiffen up when not used for so many years. If you want to try, the first step is to figure out how to get the top cover off. If you can do that, you can oil the part that appears stuck. It can take quite awhile for the oil to penetrate, so you may have to do that repeatedly. If there is gunked up oil in there, you may need to use some kind of cleaner to remove the gunked up oil. Sorry this is very unscientific! If you can find websites that detail how to free up the handwheel on a sewing machine, the same information should apply to a serger.
It would probably be a good idea for you to join a group such as wefixit on groups.yahoo.com to get better technical advice. A husqvarna sewing machine group could be helpful too. A lot of time there are technicians on these groups who can provide you with basic information.