Nothing wrong with fiddling with partitions, you just do not know how to do it safely yet, and that is how we all learn, by breaking stuff!
I have not used a Hiren Boot CD in ages, so do not know if it is capable of fixing the boot loader.
You see, you need a boot loader, no matter what OS you use (Windows, Mac, Linux) and all you now need to do is install the Windows boot loader again, therefore the steps mentioned by seymour7, fixmbr and fixboot.
Ring up a friend and see if someone can lend you a XP CD for 5 minutes if you REALLY lost your original, or if you have a valid license, make yourself a copy from a friend.