The host although cheap looks very limited in what they are offering for the money.
If you wish to install scripts such a Pixelpost you may be better to find a host that offers cPanel and maybe Simple Scrips, options that I don't see offered by Streamline.
I would take a guess that to get Pixelpost onto Strealine, you would need to download the install script to you computer then use an ftp client to upload it to your streamline domain. You would also need to create a MySQL database then point your browser at the install script and follow the instructions to get it installed.
With a host that has SimpleScripts you could just log on to cPanel, chose SimpleScripts and then chose to install Pixelpost from the list of available scripts. The MySQL database is then created for you as part of the installation.
If you want to play with Pixelpost before you commit to anything I can host it for you and give you an admin account so you can test it.