WireMod
1. Find your GMod addons folder -
\Program Files\Steam\steamapps\<account name>\garrysmod\garrysmod\addons
2. Go to http://www.wiremod.com/forum/wiremod-general-chat/4-wiremod-svn-guide.html
and find the linked called Tortoise autolink. Click it.
3. This should open up TortoiseSVN and set it up for the repo. In the second box
(Checkout directory), remove whatever it says and paste the addons folder path (above).
Click OK, and wait for it to download everything. If asked for a username and password,
use anonsvn / anonsvn. This will install WireMod.
PHX3
1. Make a folder in your addons folder called phx3.
2. Right-click this folder and select SVN Checkout.
3. Put https://phoenix-storms.svn.sourceforge.net/svnroot/phoenix-storms/ in the first box
(URL of repository). Click OK, and wait as before. This will install PHX3.