For Git Bash

If you are running msysgit (I am assuming you are) and are looking to run Git Bash (I recommend it over TortoiseGit, but I lean to the CLI more than GUI now), you need to figure out what your home directory is for Git Bash by starting it then type pwd (On Windows 7, it will be something like C:\Users\phsr I think). While you're in Git Bash, you should mkdir .ssh.

After you have the home directory, and a .ssh folder under that, you want to open PuTTYgen and open the key (.ppk file) you have previously created. Once your key is open, you want to select Conversions -> Export OpenSSH key and save it to HOME\.ssh\id_rsa. After you have the key at that location, Git Bash will recognize the key and use it.

Note: Comments indicate that this doesn't work in all cases. You may need to copy the OpenSSH key to Program Files\Git\.ssh\id_rsa (or Program Files (x86)\Git\.ssh\id_rsa).

For TortoiseGit

When using TortoiseGit, you need to set the SSH key via pacey's directions. You need to do that for every repository you are using TortoiseGit with.

You could use PowerShell to update group policy. Here's an example:

set-gpregistryvalue -name "WU" -key HKLM\Software\Policies\Microsoft\Windows\WindowsUpdate -ValueName "WUServer", "WUStatusServer" -type String -Value "http://wsus01.internal.local:8530"

And here's where you can read up more on the amazingness that is powershell:

http://technet.microsoft.com/en-us/library/ee461027.aspx

OR AN EVEN BETTER ANSWER:

Step 1: Setup Active Directory
Step 2: Join computers to Active Directory domain
Step 3: Configure group policy to point computers to WSUS server
Step 4: Profit