If you have drivers beyond your control, you may need to force SQuirreL SQL to use the 32-bit java. This is my Windows 7 example, added to squirrel-sql.bat after LOCAL_JAVA was defined the default way.
@rem manually setting the path so we force 32-bit java, which is necessary @rem because of us using the old Progress JDBC drivers, and Merant 32-bit ODBC @rem drivers set LOCAL_JAVA=c:\Program Files (x86)\Java\jre7\bin\javaw.exe