What kit did you get at Sam's club? You have probably already bought it but the best type of liner is EPDM? rubber liner. It's that most other liners will be brittle and break over years because of the UV from the sun. Here are a few to check out.
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=2003539826
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=2002922636
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=2003602970
Now in order to keep some fish past summer, you have to have a pond that should be at least 24" deep (2ft) otherwise it will freeze over. More than that could be even better. I believe they recommend heating it or using a deicer, if it gets below 0 degrees.
However, if it's only a temporary summer thing, than have you decided where to put your fish once winter hits? People do keep koi in the winter months also.
However, the only fish I would know that would work for the winter months are crappies, bluegills, catfishes, perches, etc. The one's you catch in PA while your fishing.
Hehe I use to live in PA.