You need to move that boot flag - should be able to do it from gparted, although I've never tried. Remove it from sda1 (Linux doesn't need/use it), and try the Windoze install again.
If that still fails, try adding the boot flag to sda3 and try again.

Just tried it. =/ didnt work.
First i removed the bot flag , and tried to install windows but it still wont detect my hdd.
then i tried putting the boot flag to sda3, but still, its the same. Windows wont detect my hdd.

:<

DO NOT use the 1995 fat32 disk format( for one thing there is a 3.999 Gig file size limit) .Ubuntu ,like all other Linux's can READ AND WRIGHT to ntfs .Just install ntsf-3g

Hmm my main problem is that the windows xp installer is not detecting my HDD =/
I just checked again in Gparted. I only see NTFS no :NTFS -3g

ntfs-3g is the program to read/wright to a ntfs file system
--------------------
and the win installer throughing an error when there is a NON microsoft file system/ os on the disk is a very well known microsoft installer cd problem.
this how to is for fedora but should work for Ubuntu
http://forums.fedoraforum.org/showthread.php?t=167302

Nothing to do with this - ntfs-3g is a *Linux* userspace application. The OP is trying to get the Windows install disk to boot.

Best I can now suggest is to zero the boot record and partition table of the disk. You'll lose everything on the disk - the installer will see as an unused disk, and proceed to use it. After that you can re-try a Linux distro (dual boot) if you feel like it. From a Linux liveCD terminal (as root/sudo), do the following - this will effectively trash your disk...

So, the plan here is to format the HDD completely, using a linux live cd then going on the live-cd terminal to type the command.
Then next step to install windows.
then after installing windows re-install the linux distro with dual booting options.

Am i right? I just hope after trashing the HDD windows installer will do work and find my HDD. or else..... :<

Yes, do as instructed to zero your drive then proceed to install winblows first then GNU/Linux after.

To be precise, that command was specifically constructed to only zap 510 bytes - the (Linux) loader code and partition table as I mentioned. The disk id bytes and all the data was retained - as a last resort the partitions could be recreated, and the data retrieved. But only if the re-install fails - once that starts, all the data will be lost.
We're here to look after you .... :)

I regularly have to do this to my test disks - XP finds the disk(s) fine. The only issue you may have is if the XP disk needs driver(s) for the disk controller; you'll need to supply that separately. Unlikely.

Hmmm weird.
i did the and then tried to install windows xp and i was still getting the same error. T^T , cant detect my HDD.
Now i had to re-install ubuntu. =x

What could be wrong? =x

You are trying to install with a full XP cd and not some cutdown OEM version aren't you? Can you boot off the XP cd?

Yeah it was a full xp cd.


OK now i think i know whats was wrong.
I just read that XP wont recognise SATA HDD -___________-
and thats why it wont detect my HDD.
I am now making a new XP installer CD from my Friend's laptop.
Hopefully it will work.

lol, sry guys my bad.