Help with drive partitions?

Hi there, I am reasonably new to disk partitioning, and I would like I few pointers. I have currently got the following configuration:

Primary partition for Win XP;
Primary partition for SUSE Linux;
Primary partition for Express Media Player (came with the laptop);
Primary partition for Linux Swap.

I am looking to add Windows Vista to my list of OS's, and also seperating all my files from my Win XP partition.

Now obviously the problem is that I've already got 4 Primary partitions. I boot from 3 of them (well, GRUB handles Windows and SUSE, there's a different button on my laptop to load with Express Media Player).

So, to the questions. Firstly will Vista (and XP) be able to see the partition I make for my data? I read somewhere that Windows ignores all but the active partition, is this regardless of file system and does it apply to XP and Vista? (It was an old article).

If there's some way to make a partition that I can put data on so Windows and Vista can both see it (and SUSE?), then my next question is how do I go about implementing this setup? I can lose express media player but I'd rather not, is there any way to do this with an extended partition? I don't really understand them. I need to configure GRUB to work with Vista as well, and presumably reconfigure it for XP and SUSE if the process will involve changing their partitions. The reason I decided to come here instead of diving straight in is because if I need to make an extended partition I am not sure how booting from it will work (if I need to).

If you can answer both those questions and explain how to set up GRUB properly afterwards then I will be eternally grateful!! Thanks very much.

Andrew