Mac HD partition problem, can you help?

I recently created a partition on my iMac to install Snow Leopard on to.
My original partition had Lion on it but it started to run slow so i thought i would just boot in to the 2nd partition and do a clean install of Lion on to partition 2 then just delete the original partition.

I did this but now i'm stuck with 400+GB of storage that i cant use on partition 2 wich is now the primary boot disk, here is a screenshot: Screen Shot 2012-05-04 at 01.58.42.png

what i want to know is how can i get that free space to merge in to the partiton named 'Macintosh HD 2'

I think i might of messed up big time but i'm not sure as i'm new to all the re-installing OS on mac :/

can you help me out?

Did your iMac come preinstalled with Lion? The reason I ask is because I do not see a Recovery partition listed on the drive. It shows two partitions as you said but no Recovery.

chscag said:

Did your iMac come preinstalled with Lion? The reason I ask is because I do not see a Recovery partition listed on the drive. It shows two partitions as you said but no Recovery.

Click to expand...

no, it came pre-installed with Snow Leopard.
when i went in to Disk Utility while on the 2nd partition i went and erased all data from the 1st and original partition, i did it without thinking.

OK, I understand. What you need to do then is boot the machine with your original Snow Leopard DVD. Run Disk Utility from the top menu "Utilities". Highlight the drive on the left side and then go to the partition tab on the right side.

Remove both partitions and then format the drive as one partition using the Mac OS Journaled file system and GUID scheme. After which you can reinstall Snow Leopard and then Lion if desired.

Or, you can create two partitions; one for SL the other for Lion. Install SL on the first partition, leaving the second for installing Lion later on. Note that if you use this method you will be unable to use Boot Camp if you should ever feel the need for installing Windows. However, you can still use VM software to install Windows.

Of course before doing any of the above, make a backup of all your data.