Ibook battery drain problem...

Hi all, I have been hunting around the various groups and forum's for a solution to my problem with an ibook. I have had no luck, so I am hoping someone here will be able to assist.
I have a g3 Ibook 900mhz 384MB Machine running a recent upgrade to Tiger. ( I cant rememebr if this problem happened with the change over, but I vaguely think it did)

I just bought a second battery for traveling e.t.c and both batteries hold about 4hrs charge. (big smile)
However I have a problem when I put the book to sleep (sad frown) When I close the lid the ibook goes into sleep mode, but for some reason it completely drains the battery.
One all occasions the battery has been almost fully charged before I closed the lid, and upon waking up my ibook I have noticed a battery drain.
My research on the fourms has not yet found someone with the same problem so I have been racking my brain trying to find out why this is the case.
is it something to do with:
A/. My airport connection? I have a wireless connection at home, is it picking this signal up and turning the HDD back on?
B/.384MB RAM, is this enough to temporarily store tiger's data? C/. A bug in the 900mhz Ibook model?

If someone can please help it would be great, I LOVE the instant sleep and wake of my book, and I dont want to have to keep shutting my system down when I am planning on leaving the item unused for a few hours.

Davin