My first was around the end of '98. Looking at the RH release history it was probably late November '98. One of the guys I chatted to on IRC burned me a copy of RH4 on CD but the computer would not read it. I figured the disc was screwy so I went out and bought a retail copy of RH5.2
At the time I was using NT4 workstation on an old (even then) 486DX2-66 with 4Mb of RAM as a mail server for myself and parents while I was at uni, on a perm dial-up link. It would take 30 seconds to check the POP account over a 10Mb LAN connection, longer if there was actually any mail. After installing RH5.2 on that machine when I checked my mail the dialog box appeared and disappeared faster than I could see it. I had to press send-and-receive a couple of times and send myself an email to believe it had actually done it!
Needless to say, I haven't use Windows on any server since.