Are you currently booting from the MBR? And, if you are, is that “/dev/sda” or “/dev/sdb”?
What you really need, is to have generic boot code installed in “/dev/sda”, set “sda1” as active, and delete all linux partitions. There’s probably a Windows XP command to put back generic boot code. If you can find that, then just set “sda1” as active, boot into WinXP and run the command to fix the booting. Then, when everything is working, delete the unneeded partitions.
The advice you have already received here from the other responders is valid, will help get you where you want to go.
However, I will make a further, refined suggestion here, and can offer follow-up help if you need it.
Disconnect the 2nd HD (sdb)
Use the partitioner of your choice (GParted, for example, but any good partitioner will do) & set your XP partition (currently listed as sda1) with the Boot flag (referred to as the Active flag in some partitioners).
Reboot & see if it loads XP. If it does, you can then reconnect your 2nd drive & repartition it.
If XP doesn’t load, I can supply you with a quick fix.
I have created my own boot CD to take care of booting into your already-installed XP, if you need it. It is perfectly legitimate, since it is only a bootable CD that has the BOOT.INI, NTDETECT.COM, and NTLDR files to locate and boot the XP on your HD.
All that is needed is to get your own XP installation to boot once. When you shut it down, it (most of the time) will check and repair its boot files. The next time you boot, XP should be working normally.
As I said, that will work most of the time. If it doesn’t work, you just boot again to your own XP from the boot CD and run your own XP’s repair functions.
If you know enough to make your own boot CD with the above 3 files, that’s great.
If not, if you need a copy of this bootable CD, let me know. I will then make the ISO available on my website & I will send you a link to download it.