Uninstalling Ubuntu
 

I have a computer that has ubuntu on it. I deleted windows XP that it originally had on it (hp compaq d220mt computer). I wan't reinstall Windows XP on it. My main computer is a mac. I installed windows xp on a usb using unetbootin. When i tried to plug the usb into the comptuter (hp compaq d220mt). I learned it was for a windows computer, it had a setup.exe file, so i guess it was for a windows computer OS :( (Sorry, im a real noob.) So is there a way to reinstall windows XP inside Ubuntu on the computer or with a usb using a mac. Thanks :)

Do you want to completely wipe away Ubuntu?

I doubt -- but do not know for sure -- that unetbootin works with Windows (XP).

Yes, I would like to completely wipe away ubuntu because it slows my machine way to much, i like ubuntu, but the computer originally was men't for windows XP, and I guess that works fine. I saw the unetbootin tutorial here ---> http://www.youtube.com/watch?v=js08DJ8FVQk so i think unetbootin works with XP.
Also i tried using wine to do the setup for installing windows (setup.exe) but i got this error, "No valid system partitions were found. Setup is unable to continue" :( is there a way to fix that?

So you're starting with a .iso file and have no cd-r available? I can't really help you there.

However, running Setup.exe from the Windows installer via wine *will not work*. You need to boot from the install cd/usb and let Windows do its thing.

Did your Compaq have a recovery partition or cd?

You need to first of all set the computer to boot from usb in your BIOS. When you boot the computer, you should see a message on the screen for 3-5 seconds telling you to press a specific key to enter setup. Press that key (HP is usually F10?) and look for the boot tab in the BIOS screen and use the keyboard arrow keys on the right to navigate to where you can set usb as first boot priority. If your computer is old enough that it came with xp installed, you may not have that option. This is the first thing you need to determine.

To determine why you got the error "no valid system partitions found" you would need to boot Ubuntu and open a terminal and run this command: sudo fdisk -l(Lower case Letter L in the command) and post the output here.

Is the iso file you have for xp service pack three as the one in the video? I've never used xp myself but, I've recently read several posts in different places of people trying to use unetbootin with xp without success. Windows doesn't recognize Linux partitions so posting the output of fdisk may give someone a clue as to what to suggest.

I tried booting it up from the usb, but all it got was a blinking " _ "
No, i don't have one :(

You need to find yourself an external USB CD/DVD drive and use that with the OEM windows disk.

That said, there's no reason you can't run Linux. Ubuntu may run slow, but that's because Ubuntu with its default DE is an absolute resource hog. There are many other choices out there that are more reliable, more stable, easier to use, faster, and less demanding. Windows XP actually has very high requirements, in fact Windows 7 without Aero actually runs faster than XP on my netbook, and both are noticeably slower than OpenSUSE with XFCE.

ok, i did sudo fdisk -l this is what i got.
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 75823103 37910528 83 Linux
/dev/sda2 75825150 78163967 1169409 5 Extended
/dev/sda5 75825152 78163967 1169408 82 Linux swap / Solaris

Disk /dev/sdb: 7822 MB, 7822376960 bytes
255 heads, 63 sectors/track, 951 cylinders, total 15278080 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/sdb1 2 15278079 7639039 b W95 FAT32
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 75823103 37910528 83 Linux
/dev/sda2 75825150 78163967 1169409 5 Extended
/dev/sda5 75825152 78163967 1169408 82 Linux swap / Solaris

Disk /dev/sdb: 7822 MB, 7822376960 bytes
255 heads, 63 sectors/track, 951 cylinders, total 15278080 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Device Boot Start End Blocks Id System
/dev/sdb1 2 15278079 7639039 b W95 FAT32

Ah yes, forgot to mention that. The slowness you're experiencing is likely a misconfiguration somewhere.

Where's the hard drive you want to install windows to? Your fdisk shows two 8GB flash drives, one with Linux filesystems and one with windows.