help! Updates killed my ibook!

Hi, has this happened to anyone? I just downloaded the lates updates from Software Update on my iBook G4, and now it just gets as far as the grey apple screen and just sits there looking like it's loading... I've given it over an hour.
Shut down, starte again, same thing...
Anyone???

run verify and repair permissions, then download update disc image from apple website rather than using software update, then everything should be fine again
find your update on this page Apple - Downloads - Mac OS X - Mac OS X Updates

if it wont start at all, start in safe mode
1 press the power button
2 Imediately after you hear tone, hold down the shift key
3 release shift key when you see grey Apple logo and spinning gear

Thanks for the advice, I'll give it a go!
Much appreciated