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?

your graphics card is supported, but shitty. Your memory will be more than enough, provided you stick to the lighter-weight WMs like xfce or blackbox. Your wireless card appears supported, but I don't know for sure and you won't unless you try it. (It's "DWL-650+", not "DWI" -- apparently uses ti acx100 driver)
Battery performance will probably be worse than windows, depending on how well acpi is supported, but the fact that you say "only three hours of battery life" is kind of weird, especially considering the laptop is at least 5 years old and thus has an aging battery.