My wife has asked me to reformat her PC! Well, I was excited until she told me she wants WinBlows again. So, anyway, I'm going to take this opportunity to make it a dual-boot system. Please help me out with these questions:

1. Which OS should I install first? I'm thinking WinBlows first and Linux second since Win has such a hard time with dual-boot systems that aren't itself. Your experiences would help, though.

2. How should I format the HDD? I know the bulk of it will be XP's native FS, but I will have a small (about 4GB) portion that is ReiserFS that keeps my Linux OS.

3. Do I have to have a separate swap partition from XP's swap partition or can both OS use the same one?

4. Any other suggestions would be welcome.

Thanks all!

You should definitely install Windows first.
I don't even know if Windows uses swap partitions.
As far as formatting... well, it depends on how big your hard drive is. Let's say, for argument's sake, that your hard drive is 20 GB.

Before installing anything, I'd partition it like this (Mandriva and Mepis include good graphical partitioning tools):

7 GB NTFS (for Windows XP)
6.5 GB FAT32 (for files to share between XP and Linux)
6 GB ReiserFS (or ext3 or whatever Linux filesystem you're using)
512 MB swap (assuming you have 256 MB RAM... it all depends on how much RAM you have)

A lot of your scheme comes down to how much hard drive space you have and how much RAM you have and how much software you have installed with Windows and what Linux distribution you're using.

Also, depending again on how much HD space you have, I recommend a FAT32 partition which both OS can share. Great for MP3's/video files/photographs, scrapbooking, or even work files, etc.

Microstuffed windoze does not use a swap parttion. It uses a swap file within its own file system.
ayslu is exactly correct in what says. windoze will overwrite any other system. It beleives it has total ownership of all it surveys.
FAT32 is the best for co-ownership between the two. There are no issues with permissions etc. The swap space needs to be RAM size X 2. It can be bigger if you think you need it.