If you get the following Java error (shown below) while trying to launch Tekkit (Technic Server), then your problem might be that you have both 32-bit and 64-bit Java Runtime Environment (JRE) installed.
Error occurred during initialization of VM
Could not reserve enough space for object heap
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
If you want to check if you've got multiple / different Java versions installed then look for a "jreX" (x = version) folder in the following folders:
c:\Program Files\Java\ (64-bit version)
and
c:\Program Files (x86)\Java\ (32-bit version)
If you've got both a 32-bit and 64-bit Java version installed then you need to change the following line in Tekkits Launch.bat from
java -Xmx3G -Xms2G -jar Tekkit.jar nogui
to
"c:\Program Files\Java\jre7\bin\java" -Xmx3G -Xms2G -jar Tekkit.jar nogui
I.e. change java to "c:\Program Files\Java\jre7\bin\java"