Dell XPS M1530 - which partition can be deleted ?

I have a Dell XPS M1530, HDD 230GB, 2 GB RAM, Windows Vista Ultimate. It came preconfigured with 4 partitions :
Volume--------Layout-----Size -------File System------Status
------------------Basic-----102MB-----------------------EISA Configuration
------------------Basic----- 2.5GB-----------------------Primary
OS(C)------------Basic------220GB---------NTFS---------Primary
Recovery(D)------Basic------10 GB---------NTFS---------Primary

I want to test Windows 7 now, and my idea was to reduce the "C" partition, in view to install Windows 7 on a new partition. I reduced the "C" partition to 160 GB and got now 60 GB free for a new partition. The problem is that the harddisk has already 4 primary partitions, and I cannot create an additional new primary partition (where Windows 7 would be installed), only new logical partitions are possible. What are the 3 "special" partitions for ? Which of them could be deleted, without getting in any trouble ? Would be for instance a good idea to generate a backup image (with Acronis True Grid) of the recovery partition, and get rid of it after that ?
Thanks in advance for your help.

 

See this thread for details about your partition layout. FYI, see here for why you can't use Microsoft's partitioning tools.


Dan