Sorry about the title, but it was the best I could conjure. Anyway, I've got a Gentoo install. It formerly had a setup like so:

/dev/hda1: /home
/dev/hda2: (swap)
/dev/hda3: /boot
/dev/hda4: /

I decided, however, that I wanted to install Windows on an external hard drive. So I pop in the CD and it tells me in order to do that, I need to put some files on my main hard drive. I figure no problem. I wipe hda3 and shove its files onto my root partition. I go through the hell of fixing up grub and everything after that, and my Gentoo system is back to normal. After that, I had hda1, 2, and 4. I tried again, and the Windows CD told me I had the maximum number of partitions. I figured perhaps because of the numbering, it thought I had 4. So I shuffle stuff around again, so now I'm left with:

/dev/hda1: /
/dev/hda2: (swap)
/dev/hda3: /home

I figure this will work. I go to install Windows again (mind you on the external drive) and I get the same message about there being the maximum number of partitions on my hard drive. Now, I know the maximum is 4, so why is it doing this to me? Please help me out.

To start with, you don't say if the three Linux partitions are made and formated as Primary partitions. You can have 4 Primary partitions, tops. Any more, you have to give up a Primary and make and Extended, then make Logical partitions in the Extended partition.

It seems that windoze is counting the Swap partition as a Primary (counting as number of partiions, and ignoring the partition type). Windoze fault; not Linux).

To get windoze on the external drive, you may have to disconnect the internal drive before trying to install. Assuming installation is successful, reconnect the internal drive, then edit your bootloader config to add windoze.

Sorry, I figured I might have provided too much information rather than too little. Anyway, my swap is obviously a Linux swap, and my (originally three) now two other used partitions are ReiserFS. They're all primary partitions. That leaves me with three used primary partitions, and one non-used partition. My external drive, just in case it's relevant, has two partitions, at approximately 60G each. One is currently ReiserFS, and one is ext3. The latter one is going to be used by Windows, and I believe Windows will take care of making it NTFS. However, I haven't yet been allowed to get to that point in the install process.