Maybe... if the data from the second partition can fit on the first, then you can do the following:
1) Copy the data from the second to first, either by a finder copy, or better yet using Disk Utility.
2) Delete the second partition.
3) Expand the first partition to take up all the space.
If you can't fit the data from the second on the first, then without another volume/disk to hold the data temporarily, then the built-in tools from Apple can't help you.
I can offer one other possibility, but one I have not tried myself:
GParted claims to be able to move HFS+ partitions, so you could use their live CD to move the volume forward, then use Disk Utility to grow it to the right size. I have to sound the large note of caution that I have never tried this, so you might lose all of your data.