e36 radio removal tool
Some have successfully loosened those screws with a small straight blade or a close-sized hex key, but mine were too tight for that. I had to have the 5-sided tool that fit.
Several on-line BMW part suppliers sell this tool for around $15, but the least expensive source is Richard Mix. He made one for me about 5 years ago. I think I paid only about $5, and I have used it several times on my two e36s. Send an email to Z3Richard [at] aol [dot] com