There is an easy way and a hard(er) way to do this. I have always had to do it the hard way myself. (I had a Windows XP Home and Windows ME setup. Now I have a dual-boot with two copies of XP. This will work regardless.)
If you can load an os, right-click on My Computer and choose Properties. Click on the Advanced tab. At the bottom there should be a section for Startup and Recovery and a Settings button. Push it. A window will come up with System Startup at the top. Then it says ‘Default operating system’ with what should be a list of all your os choices in a dropdown menu. Then it has some other options there. Anyway hit the Edit button, and your ‘boot.ini’ file will appear in Notepad. It should look similar to this:
[boot loader]
timeout=5
default=multi(0)disk(0)rdisk(1)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(1)partition(1)\WINDOWS="Microsoft Windows XP Home Small" /fastdetect
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Big" /fastdetect
Timeout is timer in seconds for how long you want the computer to show you a list of operating systems to choose from before it loads the default. Default is just what it sounds like and then you see all your choices, which should be one for you right now. The 'multi(0)disk(0)rdisk(0)partition(1)\WINDOWS=â€Microsoft… Blah Blah Blah' lines are important. The rdisk(#) is talking about physical hard drives. (0) is C: and (1) is D: etc. On my setup, for instance, I am booting from my D: drive. Everything in the double quotes is what you will see when you turn on your computer. Delete two whole lines (that start with 'multi') and make sure to change the rdisk(#) to 0 (see note). Change the name of the os to what you will. Save your changes and restart. That’s it.
Note:
If your Windows install is on your C: partition, use 0, if it is on D: partition, use 1, and if it is on your E: partition, use 2. Also note that i have two physical drives with one partition apiece in this example. You may need to change the # for the partition instead of the rdisk. In any case you are probably booting from the C: partition, in which case the line should look like this:
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft... blah, blah, blah"
I do not know what '/fastdetect' does, but I would leave it there.