Creating a partition for ubuntu with 4 windows partitions

Few questions: Are you switching to Ubuntu? If yes, then you might want to club two partitions that give you maximum space. I'm pretty sure that you can add more partitions if there's space. Have you already consumed all the space on your disk?. HP tools and system seem to be your options.

No I am not switching to ubuntu, I want to install it on a separate partition, and of course windows will still be installed on another partition.
I had a spacy C: partition which I divided in two as you can see:



The problem is, when I was wanted to install ubuntu on the free space I created, I couldn't because you cannot have more than 4 principal partitions. Then I thought I might solve the problem by deleting one of the small partitions I still have, but it was risky because you never know what might happen if you get rid of one. I did a search on the internet to get an idea about what could happen, and most of the people were saying that it's better not to delete the HP Tools partition. Obviously, the System partition is not an option either, so I am left with the possibility of making cds or dvds of recovery after which I delete the recovery partition. And to be honest, I would prefer to do something safer like clubbing two partitions, but I don't know how.