Well when I converted my 1.2.5 vanilla SSP to 1.2.5 Tekkit SMP, I went off looking for the end.
Found a portal, went through it, to find a dragonless world... oh, and the portal dropped me off on a small platform in the void, several thousand blocks from where the end land actually was. Interestingly and as an aside, whilst searching for the end land, I found a number of oils wells just gushing forth from into and from the void.
Thinking it was a bug I read the Minecraft wiki, and would swear it said SMP the end doesn't generate at all, but if you convert a world you can do there, but its dead. It doesn't say that now, but I do remember reading stuff somewhere that exactly correlated to my experience, so I mined some end stone and use my OP powers to come home.