I did the hood strut replacement in a 99 I30 a couple of years ago. I used the OEM parts from IoS,
http://www.infinitipartsusa.com They were expensive, $200+ a pair. Unfortunately the ball mount does not come with the new strut. You need a power tool to cut the socket to free the ball mount rrom the old strut.
So when I needed to replace the struts in my Q45 2 months ago, I followed Brian's (maxmix) advice and bought an OEM-equivalent struts - a pair for @ $58 including shipping. I think the brand name is Tuff Support and bought them from "partsavenue.us." The assembly includes the ball mounts so you don't have to do any cutting. They should have struts for 99 Maxima.
I always replace the struts in pair. You may need somebody or something to prop the hood up. In my case, I used a vise grip on the old strut to keep the hood up while I work on the other strut. DO NOT USE A VISE GRIP ON A NEW OR GOOD STRUT AS IT CAN DAMAGE THE ASSEMBLY. If you have to, make sure you have a rag around it to protect the strut from damage.
Rod