Ubunto on old Toshiba Satellite?

I have a old laptop running Windows XP.

It has 320mb memory.
650mhz Celeron.
Savage S3 video card.
6gb Disk space.
DLink DWI-650+ Wireless card.

I want to put Ubuntu on it. I've heard bad things about Linux and laptops.

This thing only gets 3 hours of battery on Windows XP when idle, will there be a difference using Ubuntu? Will it be more responsive? Does the default install take less disk space than a Windows XP install. Space is at a premium for me on this thing. Is there anything else I should know about putting Linux on my laptop?

I have a slightly older laptop, but similar (it's a satellite 2180CDT) and Ubuntu works fine on it, except for the fact that the video card is shitty enough that I can't run at more than 640x480, which is a big issue when your monitor goes "wiggly" unless it's in 800x600. how much VRAM does the video card have? that's the maiin issue I had, because mine has 2MB and is essentially useless. (it doesn't even support OpenGL :O!)