Is it tough to replace the rear struts on a 1999 Hyundai Accent?

Yes, and potentially dangerous. Better to have a shop do it if you're not familiar with cars (you'll need a spring compressor if just replacing the shock, but an impact wrench is a must whether your replacing the shock or the whole strut). However, the service manuals for Hyundai can be found on line at http://www.hmaservice.com/webtech/ Click on the "shop" tab, choose your car and find the information you are looking for. More information can be found at: http://www.hyundaiperformance.com/forums/topic.php?t=24629