Toast problem burning discs & ichat.hard drive space?

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I have an iBook G4. 1.33GHz processor & 1.25 GB memory. i've had this machine for a little over a year.

Recently, Toast crashes everytime i try to burn a full 4G dvd. I've burned plenty of dvd's in the past, but only recently had a problem. the superdrive and toast seem to be working because it will let me burn a cd as well as a dvd up to 2GB. the finder was giving me a pop-up telling me that i needed more disk space equal to the disc i was burning. I cleaned off some space and now I have 8GB open on my computer and it still won't work. I ran the disk utility to try to clean up some space, but that didn't work either. I've burned full dvd's with less than 500 MB... i don't understand what the problem is now.

I was also noticing that when i do the apple-I function to calculate the size of a folder, it doesn't always bring up the correct size right away. sometimes the updated folder and hard drive space doesn't show until later.

Also, I've been having problems with ichat recently. i frequently get disconnected even though my internet connection stays intact. i can't seem to stay connected for any length of time.