Rejoin 2 partitions

I previously had 2 partitions on my Mac on a 500g hard drive I partitioned 100gb as my working drive and 400gb as my backup drive.

However I now have an external drive for all my backup data and as Bootcamp will not work with partitions.

So how do i get them back as 1 drive/partition so i can go back to using bootcamp?

And will this work without having to reinstall OSX?

What version of OS are u using? For Leopard, you don't need to erase the whole hard drive to do that. You just go to disk Utility/partition and revert it. However, for older version mac, you do need to erase and format the HD to revert the partition. However, as I know, bootcamp do need to partition your drive for the window part. As they are different OS, you can put them on the same part of the HD to work. You just need to install your window using the 100gb partition. It should be fine.

Partitions

It is the lastest OS I am running

I already tried boot camp and gave me the error "The startup disk must be formatted as a single Mac OS Extended (Journaled) volume or already partitioned by Boot Camp Assistant for installing Windows."

I will join them back together just finishing up copy my data