The battery for my MacBook seems to be buckled, so that the MacBook doesn't sit flush on the table top.

What it all Means it that your Battery is swelling up, Here is the link to the replacement battery:

http://store.apple.com/us/product/MA561LL/A/rechargeable-battery-13-inch-macbook -white?fnode=5a

You can get a new third party battery fairly cheap on eBay. Every MacBook from 2006 through Mid 2009 except the Late 2008 Aluminum Unibody and the Late 2009 and 2010 White Unibodies use the same A1185 battery.

Black Batteries http://shop.ebay.com/i.html?_nkw=macbook+black+battery&_sacat=0&LH_BIN=1&_sop=12 &_dmpt=Laptop_Batteries&_odkw=macbook+white+battery&_osacat=0&_trksid=p3286.c0. m 270.l1313

White Batteries http://shop.ebay.com/i.html?_nkw=macbook+white+battery&_sacat=0&LH_BIN=1&_sop=12 &_dmpt=Laptop_Batteries&_odkw=macbook+black+battery&_osacat=0&_trksid=p3286.c0. m 270.l1313

Or for $129 from The Apple Store http://store.apple.com/us/product/MA566LL/A?mco=MTY3ODQ5OTY

Get that thing out of there as soon as possible. It will cause damage to your trackpad and other items in the MacBook.