i have dual boot system, it used to be triple. i am using vista's bcdedit. you can do it this way if you want.
if i understood you right, you installed leo, but you cant boot into it anymore ? can you boot into Vista? Usually when leo overwrites mbr you cant boot into vista either - so you have to use vista dvd, go to repair, pick 'startup repair' and you'll have it fixed and the path to winload.exe is back again.
Now, when you can boot into win, use EasyBCD and remove the entry you added earlier, we will add it from scratch. Just leave first and default option for Vista. Launch command promt, start->run type cmd <enter>

bcdedit <enter> will list all of your entries and the values

bcdedit /create /d “Mac OS X” /application BOOTSECTOR
--this will create and return an ID for this entry. like {81ed7925-47ee-11db-bd26-cbb4e160eb27}. this will be your {macid}
you will replace it later in the next steps with the ID you got. right click on cmd promt, MARK, and select it including the {} brackets.
you can use PASTE for your {macid} (not ctrl+v while in cmd promt, right click and then paste)

bcdedit /set {macid} device boot

bcdedit /set {macid} PATH \chain0

bcdedit /displayorder {macid} /addlast

bcdedit /timeout 10
---
thats it, added in vista boot manager so you can select vista or mac os x to boot. before starting this, copy chain0 to the root of your Vista, root of C drive.

Hope it will help.

---