changed user path and lost aliases in .bash_profile
I think these are not related. What you're seeing is the default bash prompt, which is defined in /etc/bashrc:

$ grep PS1=  /etc/bashrc
PS1='\h:\W \u\$ '


From the bash man page:

 \h     the hostname up to the first `.'
 \u     the username of the current user
 \W     the basename of the current working directory, with $HOME abbreviated with a tilde


What's happened is that your hostname is not being set correctly. It related to your network settings. It was discussed on superuser: https://superuser.com/questions/318509/hostname-issue-in-mac-os-x-lion

And on the /etc/paths.d/git file, what you did is correct. If you have git installed in /usr/local/git/bin, then the install usually creates that file for you. But the contents are trivial, so you can create it yourself. It should have a single line, containing the path to the bin directory you want added to PATH for all users:

$ ls -l /etc/paths.d/git
-rw-r--r--  1 root  wheel  19 Sep 17  2009 /etc/paths.d/git
$ od -ta /etc/paths.d/git
0000000    /   u   s   r   /   l   o   c   a   l   /   g   i   t   /   b
0000020    i   n  nl
0000023
$ wc -l /etc/paths.d/git
   1 /etc/paths.d/git
$ cat /etc/paths.d/git
/usr/local/git/bin