It may be difficult now with the drywall up, mainly cause the thickness of the wall now may be wider than the arm spread on an old work box. You may need to cut the drywall out around the area you want to install the old work box into, install the old work box and then patch around the box with joint compound, once dry you can then install a box extender to bring the face of the box out flush with the drywall surface. Here's a couple of links that'll show you how to install an old work box in a plaster and lathe wall and how to connect the receptacles.
http://www.hammerzone.com/archives/e...thick_wall.htm
http://www.hammerzone.com/archives/e...ft/connect.htm
Here's a link to show you the box extenders you'll need.
http://www.aifittings.com/m_9.htm
If you want to install a 3prong receptacle then you'll also need to verify a ground exist in the existing receptacle box and then extend a ground between the metal box and the new box you install. Here's a link that'll show how to test for a ground in your existing box.
http://www.codecheck.com/250_50_commentary.html
Be aware that if you decide to move these receptacles up the wall from the current ones installed in the baseboard. The box that is in the baseboard that this splice is made in must ALWAYS remain accessible, meaning a cover plate can be installed over the box to hide the inside of it, but you CAN NOT cover this box with a piece of baseboard to hide it in the wall. It must always remain accessible.
You should also get your self a good book on electrical household wiring. The Black and Decker book to Homewiring is an excellent resource with lots of pictures and diagrams to teach you the basics.