Hmmm, let's get our facts straight here.
You say you have two partitions, is that correct?
And that - when viewing in Disk Utility - the [now deleted] Tiger partition was the "first" one? That is, the "uppermost" one?
And - the Leopard partition is the "lower" one?
Is all this correct?
And that there is now nothing on the upper partition? And that the lower partition is now the System you want to keep?
Why don't you try this:
Download either CarbonCopyCloner or SuperDuper. Either will do what you need to do, and both will do so without having to pay anything.
Use CCC or SD to "dupe" the contents of the Leopard partition to the [empty] partition (the "upper one").
Once that is done, boot from the upper partition to be sure you get a "good boot".
Next, open Disk Utility.
NOW see if you can erase, and then remove, the "lower partition".
If so, do it.
When done, all your stuff will now be "migrated" to the single partition.
- John