IBOOK G my you tube video and streaming video plays jerky and slow?

Here are my computer specs The iBook G3/900 (Early 2003 - Opaque White), features a 900 MHz PowerPC 750fx (G3) processor with a 512k "on chip" level 2 cache, 128 MB of RAM, a 40.0 GB Ultra ATA hard drive.... I use the airport card to connect to my home network so I can go online with the computer. The problem is that for some reason my video plays very jerky and slow and freezes up completely. You really cant even watch video on this at all unless it is on the dvd player..... Could any of you tell me what the problem might be and what I could do to fix it?