I have a question... I can't get OLC to work right. I downloaded the server and the olc version. i replaced the original rom.exe with the olc one and it still doesn't work :(
I don't know where one is, try using Google or similar to search for "rom olc patch". Applying patches is best done if you are familiar with compiling in C, otherwise minor error messages are going to confuse you.
As for ROM and Diku, ROM is a derivation of Diku. There used to be a nice chart on www.smaug.org, but I can't find it right now. In other words, Diku came first, and ROM was an enhanced version.