If IPB skin installs are anything like vBulletin then it's fairly easy if the skin is already made. All you'll basically have to do is upload the skin images to a specific folder on your website then import the skin installation file (vB uses an XML file for that).
To find pre-made skins just search on google for "IPB skins" or "free IPB skins."
http://ipb-skins.org/ is one that I found.
