I know that there exists a command line option, -vm, to specify the path to the executable of the Java runtime. This may be the same as in eclipse.ini.
There are two ways the JVM can be started: by forking it in a separate process from the Eclipse launcher, or by loading it in-process using the JNI invocation API.
If you specify -vm with a path to the actual java(w).exe, then the JVM will be forked in a separate process. You can also specify -vm with a path to the jvm.dll so that the JVM is loaded in the same process:
You can also specify the path to the jre/bin folder itself.
Note also, the general format of the eclipse.ini is each argument on a separate line. It won't work if you put the "-vm" and the path on the same line.
I am not sure if something has changed, but I just tried the other answers regarding entries in "eclipse.ini" for Eclipse Galileo SR2 (Windows XP SR3) and none worked. Java is jdk1.6.0_18 and is the default Windows install. Things improved when I dropped "\javaw.exe" from the path.
Also, I can't thank enough the mention that -vm needs to be first line in the ini file. I believe that really helped me out.
Thus my eclipse.ini file starts with:
-vm
C:\Program Files\Java\jdk1.6.0_18\bin
FYI, my particular need to specify launching Eclipse with a JDK arose from my wanting to work with the m2eclipse plugin.
Assuming you have a jre folder, which contains bin, lib, etc files copied from a Java Runtime distribution, in the same folder as eclipse.ini, you can set in your eclilpse.ini