If you really have Windows 7 64 bit, the most common source of the problem is running 32-bit Java only. You can test it simply typing
at the command prompt. The response should be something like this:
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02, mixed mode)
for 64-bit version of Java. Note the "64-Bit" phrase at the last line.
If your Java version is not 64-bit, simply download and install 64-bit Java from
http://java.com/download (click "All java downloads" on the left side and select Windows offline 64bit). Finally, point your Osm2garmin installation to the newly installed Java - see instructions in the FAQ. If you will be successful, no memory adjustments will be needed most probably and your Osm2garmin installation will run with the best performance possible.