I'm dual booting Vista and XP right now using Vista Boot Pro. I have no problems with Vista but when I try to boot into XP it tells me hal.dll is missing or corrupt. I tried replacing it but it didn't work. When I restart it again it will work but then if I restart it will do it again. It does it every other time, which causes problems when trying to install programs after rebooting and stuff. Any solutions? Thanks.

Sound like the boot.ini may have changed in some way that duz the boot.ini say in it on your PC?

I searched and could not find any boot.ini file

If your in vista you need to do this the boot.ini is a hidden file it will be on the c drive most likely
1. Click the round blue Start thing in the left corner
2. Click Control Panel
3. Click Folder Options
4. Click the View tab
5. Click Show hidden files and folders
6. If you want to see system files as well, unclick Hide protected operating system files (Recommended)
7. Click OK

Ok, I did that (hidden files were already set to show, but i set os files to show as well) and I still see no boot.ini file.

All PC with XP and or Vista have a boot.ini here the full instructions from MS on how to edit it I think what your problem may be it that the boot.ini is pointing to the wrong path for XP which causes the error your having

How to edit the Boot.ini file in Windows XP

The boot.ini should look like this

If you have XP on C partition then your boot.ini should read:
[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(3)\WINDOW S
[operating systems]
multi(0)disk(0)rdisk(0)partition(3)\WINDOWS="Windo ws XP Media Center Edition" /NOEXECUTE=OPTIN /FASTDETECT

If you have XP on E partition then your boot.ini should read:

[boot loader]
timeout=30
default=multi(0)disk(0)rdisk(0)partition(2)\WINDOW S
[operating systems]
multi(0)disk(0)rdisk(0)partition(2)\WINDOWS="Windo ws XP Media Center Edition" /NOEXECUTE=OPTIN /FASTDETECT