[slashnhax]

For both, change the javaPath variable to wherever your 32-bit JRE is installed.
For Spectre, change the spectrePath variable to wherever the Spectre jar is (mine is in the same folder and named "spectre.jar").

The Spectre jar gives you the option to add arguments.
The Client jar gives you the choice of rs3(default), osrs, or dark.

Windows
Spectre (launch_spectre.bat):

@ECHO OFF
SET javaPath="%ProgramFiles(x86)%\Java\jdk1.8.0_74\bin\java.exe"
SET spectrePath="spectre.jar"
ECHO Using Java: %javaPath%
ECHO Spectre path: %spectrePath%
SET /p args=Enter Spectre arguments (-sdk etc.):
%javaPath% -jar %spectrePath% %args%

Client (launch_client.bat):

@ECHO OFF
SET javaPath="%ProgramFiles(x86)%\Java\jre1.8.0_74\bin\java.exe"
SET officialClientPath="%HOMEDRIVE%\%HOMEPATH%\jagexcache\jagexlauncher\bin\jagexappletviewer.jar"
ECHO Using Java: %javaPath%
ECHO Using Client: %officialClientPath%
SET config="http://www.runescape.com/l=en/jav_config.ws"
IF “%~1”==”” SET /p modeInput=Enter game mode [rs3(default), osrs, dark]:
ELSE SET modeInput=”%~1”
IF "%modeInput%"=="osrs" SET config="http://oldschool.runescape.com/l=en/jav_config.ws"
ELSE IF "%modeInput%"=="dark" SET config="http://www.runescape.com/jav_config_beta.ws"
ELSE SET config="http://www.runescape.com/l=en/jav_config.ws"
ECHO Using config: %config%
%javaPath% -Dsun.java2d.nodraw=true -Dcom.jagex.config=%config% -jar %officialClientPath% runescape

Linux
Spectre (launch_spectre.sh):

javaPath="java"
spectrePath="spectre.jar"
echo "Using Java: $javaPath"
echo "Spectre path: $spectrePath"
echo "Using args: $*"
$javaPath -jar $spectrePath $*

Client (launch_client.sh):

javaPath="java"
officialClientPath="$HOME/.config/runescape/bin/jagexappletviewer.jar"
echo "Using Java: $javaPath"
echo "Using Client: $officialClientPath"
if [ "$#" = "0" ]
then
echo -n "Enter game mode [rs3(default), osrs, dark]:"
read modeInput
else
modeInput="$1"
fi
if [ "$modeInput" = "osrs" ]
then
config="http://oldschool.runescape.com/l=en/jav_config.ws"
elif [ "$modeInput" = "dark" ]
then
config="http://www.runescape.com/jav_config_beta.ws"
else
config="http://www.runescape.com/l=en/jav_config.ws"
fi
echo "Using config: $config"
$javaPath -Dsun.java2d.nodraw=true -Dcom.jagex.config=$config -jar $officialClientPath runescape