You can get a new third party 60W power adapter on eBay for under $20.
http://www.ebay.com/sch/i.html?_nkw=macbook+power+adapter&_sacat=0&_sop=12&_dmpt =Apple_Laptops&_odkw=macbook+power+adapter&_osacat=111422&_trksid=p3286.c0.m270. l1313
Or for $80 from Apple http://store.apple.com/us/product/MC461LL/A?
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.
Or for $129 from The Apple Store http://store.apple.com/us/product/MA566LL/A?mco=MTY3ODQ5OTY
You can upgrade from 10.4 straight to 10.6 with no problems. Any program that runs under 10.4 should run under10.6. See this list for compatibility with 10.6: http://snowleopard.wikidot.com/
You might have to upgrade some drivers for printers, etc.... And you will have to install Rosetta if you have any Power PC applications http://www.macobserver.com/tmo/article/snow_leopard_installing_rosetta/
I recently upgraded an older MacBook (model 1,1) straight from 10.4 to 10.6.
A retail 10.5 Leopard disk will run you around $200
The Snow Leopard 10.6 DVD should still be available at this time from Apple for $19.99. You will have to call Apple Customer Care 1-800-692-7753 or 1-800-676-2775 to purchase it. It may still be in the Legacy Products list. The App Store which is required to download 10.7 Lion or 10.8 Mountain Lion is part of the 10.6.6 update.
If you wait to long and they no longer have any in stock you will have to buy it from eBay or Apple resellers that still have stock. But you will have to pay a premium since the DVDs are no longer being made. Snow Leopard DVDs are already over $100 on Amazon.
Before Mac switched to Intel processors in 2006 they used Power PC processors from 1994 to 2005. Power PC 601 through 604, G3, G4 and G5. Applications written for the Power PC processors need the application called Rosetta to run on Intel processors. This was part of the Operating System in 10.4 and 10.5 but was an optional install in 10.6. With 10.7 Lion Apple dropped all support for Power PC applications.
To see if you have any Power PC programs go to the Apple in the upper left corner and select About This Mac, then click on More Info. When System Profiler comes up select Applications under Software. Then look under Kind to see if any of your applications are listed as Power PC.