Boot.ini should be in the root, but it is usually marked as a hidden-system file. So if you do not have
the folder view set to show all files you may not see it.
Some other program may have changed something in your boot settings.
To repair it, first check for backups of the file like boot.bak or boot.1 in the root directory.
If you do not have a boot.ini, try renaming one of those files as the boot.ini file.
You may want to look at them first thru notepad or some other text editor... a proper boot.ini should
look similar to this:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(1)partition(1)\WINDOWS
[operating systems]
multi(0)disk(0)rdisk(1)partition(1)\WINDOWS="Microsoft Windows XP Professional"
if that does not work, try booting from the XP Home CD and running the recovery console, from
there try the fixboot, fixmbr and/or bootcfg commands to see if you can repair the boot setup.