Upgrading to Cisco switches

[NetEng]

I am upgrading my network from Bay/Compaq/Misc. switches to Cisco switches. I heard a rumor...in order to connect a Cisco switch (from a wiring closet) via fiber (GBIC) the core switch must also be a Cisco. In other words, a Cisco switch when connecting via fiber can only connect to another Cisco switch. I find this hard to believe, but I want to make sure before I go spouting off. Thanks in advance.