Ubuntu Installation :: Optimal Partition Sugguestions For Speed & Dual Boot With Shared Data?

I am installing a custom 8.04 live disk (basically, a mirror of my whole system with user data intact, sans all non-OS files) from a USB key with remastersys for the .iso creation, and UNetbootin for the bootable USB on a brand new 120GB PATA WD HDD. Both do nicely so far, so I have a working livedisk to use until I need to install Ubuntu to the drive.

I had a pure linux box, but I need to add XP with dual booting now- I have to use Autodesk Inventor 2010 software for my college class on my laptop, so I don't drive 30 miles to use the 1 computer lab equipped with that software. I'm not new to Linux, but I am new to more in-depth partitioning. I've taken the lead and looked into things- read this good guide, among others:

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http://www.psychocats.net/ubuntu/partitioning and noticed that there is a way to more deftly use partitions so that personal files can be shared access and write between Windows and Linux partitions- with this:
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http://www.fs-driver.org/ Ubuntu is still my main OS, but being able to access all my media/data files between the 2 systems would be nice. Problem is, until now, I've put everything on a single partition because I didn't know better. Now I do, but am a bit confused with all the guides as to what's most efficient, especially in my case where full RAM speed is crucial to running a single program.

Here's what I know I need to do: 1. The Windows XP install I know needs from 20-30GB for Inventor 2010 LT to work well. I don't need anything else in XP spacewise- it's just being added for Inventor. 2. I'd like to create a separate /home partition for Ubuntu this time to save my user data, making future upgrades much more painless (I will be getting Lucid soon). How that works when upgrading, though, I don't know yet..

3. I'd like both OSes to share all my personal files (docs, pics, music, Inventor design files) if it is an efficient choice that works without problems.

4. Finally, because 2GB is minimum for Inventor to run decently, I need to maximize the speed of my RAM for it- from my reading, these so-called "swap" partitions can somehow be added for buffering this- people seem to sugguest the swap be half the size of the RAM for fastest speed, and some say add separate /usr or other partitions. I'm not clear on what would be most efficient for me.

I have limited HDD space- because of my laptop's BIOS, this single 120GB drive is the biggest I can get on my laptop, so efficient partitioning would make a huge difference for me. Before this, a 60GB HDD was in this. I'd like to see some added space for my data storage, but still keep things as fast as possible for Inventor when I use it, and Ubuntu.