Is it better to try to partition a drive for XP and Ubuntu or is it better to have a second hard drive for Ubuntu? I was also wondering about cross compatibility between Linux and XP. Do I need to format to Fat to be able to use files in both operating systems?

i) doesn't really matter. I prefer a separate drive in case I format the wrong thing ...
ii) I use VFAT, but NTFS support is now mature. Use a separate partition for sharing rather than risking C:

A second drive is preferable; otherwise you might find your disk space getting small on XP.
The latest NTFS driver has been working very well for quite a few months now; Linux can mount your XP partition and read/write to it.

Just be careful when installing and so on; if the BIOS enumerates the disks differently when you add that second disk, you may have to physically swap the drives around to get XP and Linux to boot.

When asked where to put the bootloader, select a partition rather than the MBR. When you do this, you will probably find that Linux won't boot on restart; do not alter the BIOS settings to make it boot (the boot will fail for other reasons); instead you need to use a live CD (like your Ubuntu install CD) to change a few things and use the WinDuhs bootloader (ntldr) to load grub (or lilo - whichever one it is).

If you really want to install the bootloader to the MBR, I suggest you first back up the MBR:
1. boot from a live CD
2. assuming the XP MBR is on /dev/hda: dd if=/dev/hda of=mbr.xp.backup bs=512 count=1
store that 'mbr.xp.backup' on a USB stick or something - you'll need it if your MBR gets screwed up.
3. go ahead and install GRUB to the MBR of the XP disk

Installing to MBR is simpler, but people have complained that XP isn't happy - maybe those people have done something wrong, but better to be safe (which is why you should back up the MBR before putting the bootloader there). Personally I have never had problems with writing the bootloader to the MBR and subsequently booting WinDuhs 2k/XP.

I was thinking I should just get a second hard drive to run linux. I think this partitioning stuff can get pretty complicated.

So what would I have to do during the install in order to be able to share files across platforms?

WinXP can't see standard ext3 partitions. It can see fat32 partitions. If you don't want to use a cd or usb flash drive to transfer files from xp to linux, then during install just create a fat32 partition, and both linux and windows will see it. It will have a 2 gig file size limit though. If you don't want the hassle of another partition, you could always make /home a fat32 partition. (That was a joke, sort of, it would work though, I think.)

David

P.S. Oh, you'll always be able to grab(and put) xp stuff from linux, it's just the grabbing linux files from xp that is the problem. There is a program that can do that for you, but when I tried it, a few years ago, it screwed a bunch of stuff up. Maybe they've fixed those problems, or maybe I just broke some things myself, but I don't trust it.

With 2 hard drives, I prefer to put all the OSes on one, and use the other for shared data. I use EXT3 for shared data--one the rare occasion that I boot into Windows, I access the EXT3 partition(s) using the ext2fsd driver.

This is actually one of the easiest things--I recommend you take the time to learn it.