If you don't have the Apple mini VGA to VGA adapter, you'll need one of those:
http://www.gomacpro.com/apple-mini-vga-to-vga-adapter-for-ibook-emac-and-imac-g4/
And then a male to male VGA cable to run from that to your HDTV.
http://www.monoprice.com/products/search.asp?spcDB=10201&spcWord=Video+Cables+-+%3Cb%3EVGA%2FSVGA%3C%2Fb%3E&keyword=vga%20cable
Monoprice is a great place for cables of all types, however they do not have the mini-VGA to VGA cable, so I linked to another site above. Check around, that might not be the best price, it's just the first one with a clear photo and explanation of what it is.
Monoprice has the VGA cables in every length imaginable.
Also note, that "officially" Apple only permitted mirroring of the iBook's display to another display, but there are supposedly hacks out there to allow use as a second display. I'm not familiar with that so can't help you, but again, the limited VRAM of that iBook likely wouldn't play well with a second display. You'd probably get lag and very poor frames per second on video, dropped video, etc., which you might get on mirroring too.
It will probably cost you $20-25 to get both cables with shipping to try mirroring on the HDTV. The good news though is you'll have the cables and be able to use the iBook with a larger display even if it's just a larger screen monitor instead of the TV.