You need a retail copy of any 10.4. A quick Google gives the full price of over $200. Ebay and Craigslist are cheaper. Seems expensive. Did you get the install disks for any version of 10.4? If so, you could Archive and Install the system again and update from Apple. After working, remember to remove the Previous System. -Ken on his 2009 early white MacBook at 10.5.7, now 25% cheaper.
All you need is a 10.4 install all the drivers for apple will be on it. This is different than a standard PC. The person you bought it from probably sold that seperate on ebay knowing you would need it and it isnt in his discription so he doesnt have to send it to you. Again any 10.4 retail cd should work for you and can be found just as cheap around the internet. My question is though does the computer not work?
Hello The OS is to be installed from the DVD or CD, and there are no place on the web to download this legaly... For the drivers, there is no need for a driver CD as all drivers are included in the OS. I would suggest a call back to the seller, or that you buy the Mac OS X Tiger separately. Apple won't give you a free DVD as it is second hand and they are not responsible of what the seller sends. Another solution is to go to an apple shop, and ask for an OS reinstall. The best would be to ask a friend however. Was the mac sold without any OS installed on the disk?