There are mainly two kinds of Emulators for downloading, which are Concept Emulator and Device Emulator. Nokia will first realse Concept Emulators for different categories (series30, series40 and series60), so developers can test their applications before the physical devices be released. There might be some updates and changes of software after devices be released, then Nokia launchs another Emulator, which should behave exactly same as the physical device in market.
In this case, Nokia Series 60 MIDP Concept SDK Beta 0.1 supports the button layout of Nokia 3650 as well as new Java APIs (Wireless Messaging API and Mobile Media API). It is for developers to test their applications before Nokia launch 3650.
Nokia Series 60 MIDP SDK Beta 0.1 for Symbian OS is designed for Nokia 7650. I recommend you to download this SDK.
I am using both, but mostly the S60Concept even though I am developing for N7650. The S60 is very buggy, no sound, a lot of crashes, no titles for screens, wrong menu entries, etc you can hardly use it.
The S60Concept is working not bad, the only difference is, that it has not the keyboard layout of the 7560, but in most cases this doesn't matter. The screen is absolutly the same.
Just don't use the 2 new APIs which N7650 doesn't support. Ah, and don't print out too much to the console, because it will slow down the S60C extremly.